Nitrogen-doped silicon indium zinc oxide (N-SIZO) thin film transistor (TFTs) were fabricated depending on nitrogen contents. It has been observed that nitrogen has substituted oxygen in N-SIZO system. Its electrical property and bias stability can be appropriately tuned by nitrogen-doping to reduce oxygen defect states. This change is mainly caused by the substitution of O atoms by N ones. As the N content increased, the peak related to the oxygen deficiency of XPS was systematically decreased. In addition, TLM analysis confirmed that the resistance increases steadily with increasing N content. Subthreshold swing (SS) was also improved by increasing nitrogen doping. This low SS means that the total trap state is decreased. As a result, it is confirmed that the negative bias stress (NBS) test shows stability as the N content increases.