TOD: First sci-fi movie. Oh my. Sci-fi. Let me think.
Since it's lately been posted about hither and yon (especially yon), "Journey to the Center of the Earth" has been on my mind, and I well remember being taken to it at age ten. Not really sci-fi, of course.
I remember my first "King Kong" on late night television, and "House of Wax" on afternoon (black-and-white) television. Still not sci-fi, damn it.
So, first sci-fi. Ah!! Maybe "Donovan's Brain" on TV?
Still thinking.