Parametric upconversion, which can convert infrared (IR) light into the visible (VIS) band, has been regarded as a successful innovative strategy for IR detection. However, the traditional upconversion technique can get only intensity information of IR light, while completely dropping its polarization information. In this paper, we present a nonlinear polarization imaging technique based on parametric upconversion that can decipher near-IR (NIR) light polarization from that of upconverted VIS waves. Assisted by the parametric upconversion process in a nanometers thin lithium niobate film, the polarization states of NIR fundamental frequency (FF) light are encoded into the generated VIS wave. Based on the nonlinear Stokes–Mueller formalism developed here, FF polarization is successfully retrieved from upconverted VIS light. High-precision polarization imaging over various targets is demonstrated using our technique, which provides a fresh perspective on manufacturing novel polarimeters for various NIR polarization imaging and metrological applications.