This study is an investigation of the propeller slipstream interference with wing aerodynamic characteristics at low Reynolds numbers. Wind tunnel testing was performed using a wing model of the NACA0012 airfoil and a two-blade propeller. The propeller was mounted in a tractor configuration. The Reynolds number was set at 4.0 × 104 based on the wing chord. Aerodynamic characteristics were measured using a three-component force balance for various propeller rotation speeds. The flow field on the wing surface was visualized by using Temperature-Sensitive Paint. This flow visualization technique is based on the difference between the heat transfer coefficients in laminar and turbulent flows. The results show that the propeller slipstream prevents flow separation. A laminar separation bubble is not formed, and therefore, the lift coefficient changes linearly and the drag coefficient is reduced.