Kotaro Honda (24.03.1870-12.02.1954) was a Japanese physicist. He was born in Tohoku. He graduated from the University of Tokyo (1897), where he was a lecturer from 1901 (in 1907 — 11 he furthered his studies in Göttingen and Berlin). In 1911—33 he was professor, and in 1934—40 president, of Tohoku University, and in 1919 — 33 and 1944—47 also director of the Institute of Steel.
His main research was in the field of magnetism and the physics of metals and alloys. He invented a number of steel grades, in particular KS steel, and gave (1917) a method of producing it.