Tosio Kato (加藤 敏夫, Katō Toshio, August 25, 1917 – October 2, 1999) was a Japanese mathematician who worked with partial differential equations, mathematical physics and functional analysis.

Kato studied physics and received his undergraduate degree in 1941 at the Imperial University of Tokyo.

[1][2] Kato is also known for his influential book Perturbation theory of linear operators, published by Springer-Verlag.

In 1980, he won the Norbert Wiener Prize in Applied Mathematics from AMS and SIAM.

In 1970, he gave a plenary lecture at the ICM in Nice (scattering theory and perturbation of continuous spectra).