This paper is concerned with stability curves and capsizing of a ship in severe quartering waves. The effects of wave height, wave length and heading angles of ship to waves on stability curve are analytically investigated for a container ship. A time domain numerical simulation program for motions and capsizing has been used to investigate motions in a variety of wave configulations. Numerical simulations based on a mathematical model are carried out to predict critical situation leading up to capsizing of a container ship in severe quartering waves. Various phisical mechanism that could be responsible for capsize are pointed out by numerical experiments.