Bismuth oxide is prepared by a gel to crystalline conversion technique without using any surfactant. The sample calcined at two different temperatures (600 and 700°C) contains only stable monoclinic phase with the variation in crystallinity. The degradation efficiency varies with the calcination temperature and is maximum for the higher crystallinity one (600°C) having larger surface area. The optical band gap value of 2.7344(9)eV also supported that bismuth oxide is used as a visible light photocatalyst. From the photocatalytic degradation experiment it is found that the pseudo second order equation fits well for the whole range of study with higher correlation coefficient.