La1-xSrxMnO3(LSMO)/TiO2 pn heterojunctions have been successfully synthesized by RF magnetron sputtering and they exhibit good rectifying properties. The diffusion potentials increase with increasing Sr concentration, which may be attributed to the increased carrier concentration. And the diffusion potential increases with decreasing measurement temperature, which may have resulted from modification of the interface electronic structure of La1-xSrxMnO3/TiO2 pn heterojunction with changing temperatures. It is worth noting that the metal-insulator (M-I) transition of LSMO can also be observed in pn heterojunctions and the increased sheet-resistance of pn heterojunctions at low temperature is related to the introduction of TiO2.