Investigation of flow characteristics at the stern is made for two stern forms : one is a newly-developed asymmetric stern of the letter-C-type and the other is its parent stern having usual form. Velocity distributions are measured by five-hole pilot tube at the propeller location for the two forms. Discussion is made about the flow characteristics including vorticity distributions, energy saving mechanism due to inflow rotation, and induced drag, etc. A new formula is presented for calculating induced drag due to longitudinal vortices. Discussion is also made for scale effect of induced drag.