"Wherever it has been shown, “Bwana Devil” has attracted much interest, has brought gold to the box office and has caused practically every major producer in Hollywood to announce plans for 3-D film. Oboler will go down in the annals of Hollywood as the man who pioneered in 3-D films, since he is the first producer to use the Gunzburg Natural Vision process on a feature-length film."

-NYdailynews February 19th 1953

You can read more about this movie here  . It might not be the first 3D movie ever , which is The Power of Love but Bwana Man is probably the first widely released 3D movie . 

You can see a trailer for this movie here or below :

Source : NYdailynews.com