In recent years, inkjet printing has been widely used in the field of flexible sensor preparation. However, the effects of inkjet printing parameters and post-processing conditions on sensor performance have not been systematically investigated. Simple fabrication and optimized performance are eagerly desired for the practical use of temperature sensors in wearable healthcare devices. Herein, we report the resistive flexible temperature sensor fabricated on polyethylene terephthalate (PET) substrates with silver nanoparticles (AgNPs)-based ink using an inkjet printer. We have thoroughly investigated and optimized the sensitivity and linearity between the resistance and temperature of inkjet-printed temperature sensors by adjusting droplet spacing and curing conditions (temperature and time). In conclusion, the droplet spacing of 20 µm and the curing condition of 30 min at 150 °C were determined as the optimized parameters. With optimized process parameters, the temperature sensor has a high sensitivity of 0.084 °C−1 and a linear coefficient of 0.999 between relative resistance and temperature in the range of 30 °C–100 °C. Furthermore, it has a fast response time (7 s) and high stability against repeated bending deformation of 500 cycles. The prepared wearable sensors have potential application prospects in temperature monitoring.