The green slime creatures were played by Japanese children in bulky monster suits.

This was the first film ever to be featured on the cult TV series Mystery Science Theatre 3000 (1988). An edited version of the film appeared on the show's never-aired pilot episode.

As composer Charles Fox explained in his book "Killing Me Softly: My Life in Music", he was hired to track existing music into the U.S. re-cut of the film since there was no budget to do a new score. He agreed, with hesitation and insistence he not be credited. The film was tracked with heavily edited music from various composers, including cues from the original composer and even existing pieces by Fox, but much to his surprise the film opened with his name not only credited, but credited as the composer.

Many of the background players are American military personnel who were based in Japan at the time.

The opening score would be recycled into a U.S. television commercial for Jade East.

Charles Fox, who wrote the theme song for this film, also co-wrote the songs for another sci/fi flick of 1968, Barbarella (1968).

The Japanese language version runs 77 minutes by eliminating the love triangle subplot between the three leads.

The UNSC headquarters on Earth shown near the beginning of the film is called "Lowry Field" in the foreground subtitle. In real life "Lowry Field" was located in Denver, Colorado and was better known as Lowry Air Force Base. Science fiction author Robert A. Heinlein also used Lowry Field as a rocket base in his novel "The Man Who Sold the Moon," which may be where the script writer for The Green Slime got the idea. In real life, Lowry Field/Air Force Base was an airfield, a base for ICBMs and a military and naval intelligence analysis center. Lowry AFB was mostly closed beginning in the late 1990s (except for a DFAS building serving veterans and service people at Buckley AFB) and has since almost entirely become a "planned community" featuring mostly upscale single family homes and condominiums.

This film is listed among The 100 Most Amusingly Bad Movies Ever Made in Golden Raspberry Award founder John Wilson's book THE OFFICIAL RAZZIE® MOVIE GUIDE.

The original storyline for The Green Slime (1968) originated in Italy, where MGM also had dealings. Years before The Green Slime went into production, MGM had contracted Italian filmmaker Antonio Margheriti to direct what was originally intended to be a series of four television movies about the adventures of a space station called Gamma One. Margheriti's films in the series consisted of I criminali della galassia (1966), I diafanoidi vengono da Marte (1966), Il pianeta errante (1966) and La morte viene dal pianeta Aytin (1967), all created over a period of three months and released in 1965. MGM was impressed with Margheriti's films and released the four films theatrically. Gamma One producers Walter Manley and Ivan Reiner were eager to take advantage of these films and made The Green Slime as an unofficial fifth entry in the film series. The only connection the film has to Margheriti's films is the space station, re-titled Gamma Three, which has a similar design as the one in Margheriti's films.

The theme song was covered by Josie Cotton on her 2007 album "Invasion of the B-Girls".

Production manager William Ross would often serve as translator between the Japanese film crew and the American actors.

The cover of 1983 science fiction book 'The Worlds of H. Beam Piper' was based on a scene on the asteroid in this movie.

In one of the most schizophrenic double features ever cobbled together, this film was doubled billed at a Long Beach, California drive-in with the romantic drama The Only Game in Town (1970).

According to the label on the promotional 45 rpm single issued by MGM Records, the theme song for the movie was written by Sherry Gaden. Randy Nauert performed on "The Green Slime Theme Song". Nauert said, "When I got back from India in 1968, our drummer, Richard Delvy was working for MGM and asked me to play sitar on this song. I can still play my part. Rick Lancelot (later with Skyoats and then Frank Zappa) is singing lead. Rob Edwards, who I'd played with since high school, is on guitar. The Theremin player is the same on the Beach Boys song "Good Vibrations". (Electro-Theremin, played by Paul Tanner). It was a long stormy night. After the session I crashed my '63 Porsche at the bottom turn, heading West on Sunset Blvd. at UCLA and Marymount."

On-screen deaths: 6.