It is clear that capsizing in rough seas is probabilistic phenomenon. But the probabilistic treatment by theoretical consideration only is very difficult. So, in this study, the probability of capsizing in short term sea condition is examined by experiments. In the first, the definition of capsizing probability is made and the distribution function of the time to capsizing ( t_c ) is assumed to become Gamma distribution. This can be obtained by the analogy of the failure of mechanical system. And the next, capsizing experiments are conducted and the above assumption is confirmed. Some examples of the probability of capsizing are obtained as shown in Fig.14. This probability is also shown by using he Weibull distribution. At the same time it is shown that those parameters representing Gamma distribution have closer relation to the significant wave height ( H _1/3) and metacentric height (GM) or dynamical stability ( D_st ) as shown in Fig. 10.