The electrical properties and microstructure of nitrogen-doped poly 3C-SiC films were studied according to different thickness. Poly 3C-SiC films were deposited by LPCVD(low pressure chemical vapor deposition) at $900^{circ}C$ and 4 Torr using $SiH_2Cl_2$ (100 %, 35 sccm) and $C_2H_2$ (5 % in $H_2$, 180 sccm) as the Si and C precursors, and $NH_3$ (5 % in $H_2$, 64 sccm) as the dopant source gas. The resistivity of the 3C-SiC films with $1,530{AA}$ of thickness was $32.7{Omega}-cm$ and decreased to $0.0129{Omega}-cm$ at $16,963{AA}$. In XRD spectra, 3C-SiC is so highly oriented along the (1 1 1) plane at $2{ heta}=35.7^{circ}$ that other peaks corresponding to SiC orientations are not presented. The measurement of resistance variations according to different thickness were carried out in the $25^{circ}C$ to $350^{circ}C$ temperature range. While the size of resistance variation decreases with increasing the films thickness, the linearity of resistance variation improved.