Microstructure change during hot deformation was studied in beta titanium alloys, Ti-10V-2Fe-3Al and Ti-15V-3Cr-3Sn-3Al. After beta solution treatments, isothermal compression was performed at various temperatures in the beta single-phase and in the (alpha+beta) two-phase region at initial strain rates between 4.2x10(-1)similar to4.2x10(-5) s(-1). When the specimens are deformed in the beta single phase region, a recovered structure was formed within beta grains although discontinuous dynamic recrystallization occurs in the vicinity of beta grain boundary. When deformation was performed in the (alpha+beta) two-phase region just below the beta transus, discontinuous recrystallization around beta grain boundary is suppressed due to the pinning effect by grain boundary alpha precipitate, resulting in a mostly recovered structure. Contrarily, when the specimen is deformed at the temperature where a large amount of alpha precipitates, dynamic continuous recrystallization occurs uniformly in beta matrix, resulting in the formation of (alpha+beta) microduplex structures containing high-angle beta boundaries. The size of recrystallized beta grain decreases as strain rate increases or deformed temperature is lowered in a good correlation with Zener-Hollomon parameter.