Transparent thin-film heater (TTFH) is an important electronic device component requiring high transmittance material and a low sheet resistance with efficient energy conversion. In general, TTFH uses indium tin oxide, but it is brittle and unstable in acidic atmospheres, along with having a slow thermal response and high cost. This condition inspires the exploration of silver nanowires (Ag NWs) as a new material for transparent heater applications. In this study, Ag NWs were synthesized via a typical polyol synthesis process and deposited on glass substrates by using a spin coating method. The thermal annealing treatment was performed at 200 °C with three different time periods (10, 20 and 30 min) to enhance the performance of TTFH. The results show that the Ag NWs were successfully synthesized with a diameter of 40-50 nm with varying lengths of 5∼15 μm. The thermal annealing treatment of 10, 20 and 30 min produces agglomerates of Ag nanoparticles, decreases the length of Ag NWs and forms the nonconductive Ag2O phase. This causes a decrease of transmittance and sheet resistance, which results in a decrease of figure-of-merit (FoM) from 204 × 10-5 ω-1 to 3 × 10-5 ω-1. The thermal annealing process also caused the temperature of the TTFH to decrease from 76.7 °C to 31.8 °C within 200 s when a voltage of 20 V was applied.