I honestly didn't know. I thought I'd either read or heard somewhere that he studied bbudhist theology at some temple somewhere and assumed that he was a buddhist. I appologise and will check on my sources.
Zach Hudson wrote:
I'm just being nitpicky, but O'Sensei wasn't Buddhist. His religion was Omoto-Kyo, which I believe is a branch of Shinto.
O-Sensei was involved for a short period of time with an esoteric sect of buddhism when he was young, and I believe it was the Mikkyo sect. They practiced a lot of meditation and mudras (interlocking fingers in different positions for meditation), etc. Later, he got into Omoto-kyo and was pretty much entirely Shinto in his beliefs.