Abstract The 3He spin analysing power of hydrogen (protons) has been measured at a c.m. energy of 20 MeV at 14 c.m. angles from 40° to 160°. The measurement of 3He target polarization was calibrated by measuring the 3He spin analysing power of 4He at an energy and angle where it was −1.00. The proton- 3He differential elastic scattering cross section is also reported at a c.m. energy of 20.0 MeV for 36 c.m. angles from 20° to 170°.