Temperature sensitive mutants (ts-mutants) are godd material for studying cell division and differentiation. Two hundred and seventy-four ts-mutants of Magnaporthe grisea were induced by UV radiation. These mutants could grow at 25℃, but not at 33℃. Pathogenicity test indicated that the pathogenicity of 32 ts-mutants reduced distinctly. Under 33℃ conditions, seven of them did not germinate, 12 stopped growing after germination and no appressorium formed, nine stopped growing after appressorium formed, for mutants formed swell and bunch appressorium, then stopped growing. The ability of perithecia formation of some mutants was changed.