Cytochrome c protein thin film possesses a high temperature coefficient of resistance. In this paper, we systematically investigated the characteristics of cytochrome c, whose absorption coefficient is 65% at wavelengths of 8~12 μm. We found that the changes in resistance resulted from surface roughness. We also discovered that, while cytochrome c improves the temperature coefficient of resistance, a pure protein solution does not conduct well. It needs a buffer solution, acting as an electrolyte, to increase electrical conductance. However, the buffer solution decreases the temperature coefficient. Therefore, optimization of the ratio of cytochrome c protein to buffer solution is required. We determined the best mixing ratio of the protein solution for a sensing material. We then designed a chip for an infrared microbolometer with a MEMS structure of suspended aluminum electrodes. The protein solution was deposited on the sensing pixel using an inkjet printer. The temperature coefficient of resistance, thermal conductance, time constant and responsivity were 25.98%/K, 7.96 × 10-5 W/K, 1.094 ms and 2.57 × 105 V/W at 2 μA bias current, respectively. We experimentally demonstrated integrating cytochrome c protein with a CMOS circuit as a sensing pixel for a longwavelength infrared microbolometer. Based on our experimental results, such a microbolometer array holds promise for the future.