The LaMnO3/graphene composites have been successfully synthesized using co-precipitation method at five different calcination temperature of LaMnO3 nanoparticles (untreated, 500°C, 600?, 700°C, and 800°C. The effects of calcination temperature on the formation of LaMnO3 nanoparticles on LaMnO3/graphene were investigated. The average grain size of LaMnO3/graphene increases with increasing calcination temperature on LaMnO3 nanoparticles. The use of calcination can effectively reduce the crystallization of LaMnO3 nanoparticles on LaMnO3/graphene composites. LaMnO3/graphene shows the orthorhombic structure of LaMnO3 nanoparticles while the peak of graphene cannot be identified owing to graphene's broad peak. The LaMnO3 nanoparticles obtained at a calcination temperature of 800°C exhibits superior adsorption to remove methylene blue. Furthermore, the adsorption test of methylene blue using LaMnO3/graphene follows a pseudo-second order kinetic process and Langmuir model.