Moria gives it 4 out of 5 stars and calls it "one of the best mad scientist films of the 1940s" and says, "it was a tour-de-force of special effects for the time it was made. The combination of matte work, split-screen and scaled-down sets is flawless." 1000 Misspent Hours praises Dekker: "who does a more than creditable job as Dr. Thorkel, and one might argue with some persuasiveness that by putting as much focus on him as he did, screenwriter Tom Kilpatrick was playing to the cast’s one real strength" and says the film
is one of the most fascinating overlooked artifacts of 40’s horror/sci-fi cinema. For one thing, it’s extremely odd to see a clunky little B-movie from 1940 being presented in luridly saturated Technicolor. But beyond that, Dr. Cyclops plays like a movie from fifteen or more years later, with a mad scientist using his radiation-harnessing machine to shrink people and animals to a fraction of their natural size.HorrorNews.net says it's "a straightforward melodrama – the pseudo-science is just an excuse to tell a fundamentally Gothic tale" and says, " It’s a fast-paced inventive film, though the dialogue is awful and the acting undistinguished, with the exception of Albert Dekker‘s portrayal of the cold-blooded, short-tempered and ruthless Doctor Thorkel". Time Out calls it "An engaging fantasy with brilliantly executed ... special effects". Rotten Tomatoes has a critics score of 100%, but the audience score is 52%.