Semiconducting Zn-Ti-Ni-O and Zn-Ti-O system were investigated. The specimens sintered at the temperature between 125$0^{circ}C$ and 145$0^{circ}C$ exhibited PTCR effect between -5$0^{circ}C$ and 35$0^{circ}C$ with resistivity ration exceeding three decades. Semiconducting Zn-Ti-Ni-O is consisted of two phases, one is n-type ZnO and the other is p-type spinel structure. The mechanism of PTCR effect was explained in relation to the piezoelectric property of ZnO and the residual stress caused by thermal expansion difference between two phases during cooling process.