$Cr_{2}O_{3}$ thick films were fabricated by screen printing method on alumina substrates and annealed at $700^{circ}C$, $800^{circ}C$, and $900^{circ}C$ in air, respectively. Structural properties examined by XRD and SEM showed (116) dominant $Cr_{2}O_{3}$ peak and increased grain sizes with the annealing. The resistance of the films decreased with increasing the annealing temperature. Gas sensing characteristics to $NH_{3}$, CO, $C_{4}H_{10}$, and NO gases showed sensitivity only to $NH_{3}$ gas. $Cr_{2}O_{3}$ thick films annealed at $700^{circ}C$ had the sensitivity of about 15 % for 100 ppm $NH_{3}$ gas at the working temperature of $300^{circ}C$. The thick films had good selectivity to the $NH_{3}$ gas. The response time to $NH_{3}$ gas was about 10 seconds.