This paper reports, for the first time, the piezoresistive effect of p-type single crystalline 3C-SiC nothin films grown by LPCVD at low temperature. Compared to thick SiC films, the gauge factors of the 80 nm and 130 nm films decreased remarkably. This result indicates that the crystal defect at the SiC/Si interface has a significant influence on the piezoresistive effect of ultra-thin film p-type 3C-SiC.