Clinical observations on Type-B Japanese encephalitit in 1953 were carrid out at Manji hospital in Yokohama. The epidemic in this year was comparatively mild falling between the violent epidemic cycles which occur every other years. Of 35 suspected cases (from thirtieth July to eleventhOctober) 27 were positvely diagnosed, the number of the true cases corresponding only to one-third of the previous year. Generally, the courses of encephalitis in this year were rather mild, and there was no case with maniac symptoms. Serum complement-fixation tests were negative in 25% of the cases. Of 27cases, 6 died, the mortality being 22%. Almost all of those with extreme disturbance of consciousness and of those with high fever over 41°C died. In the cases where muscular spasms were frequent and those with long continued low fever were observed to manifest sequela.