Laser detectors based on manganite oxide heterojunctions of LaxCa1-xMnO3/Si, with x=0.67 and 0.40 respectively, were fabricated, and their photovoltaic effects were investigated induced by 532 nm and 1064 nm continuous wave laser. The photovoltage obtained in heterojunctions with good p-n characteristics were large when irradiated under 532 nm laser. The transient peak voltage of the heterojunctions were observed when the laser was turned on and off, and increased with chopping frequency and showed saturate tendency finally. Double peak in photovoltaic signals were observed in the heterojunctions when 1064 nm laser was turned on and off, which was contributed to be the combination of photovoltaic effect and thermoelectric effect.