Thick-film positive temperature coefficient (PTC) thermistor on Al2O3 ceramic substrate was prepared by laser sintering of thick-film electronic paste. The effects of laser processing parameters and the temperature of post heat processing on thick-film PTC thermistor width, surface microstructure and performance were studied. The minimum linewidth of thick-film PTC thermistor by laser sintering is 40 μm. The temperature coefficients of resistivity (TCR) of PTC thermistor is around 2965×10-6/℃, and the performance is equivalent to traditional oven-fired electrical paste. The laser power density and the temperature of post heat processing have great effect on the sheet resistivity and TCR of PTC thermistor, and there exist optimum values for these parameters.