The exposed specimens in a marine atmosphere for 10 years were examined to know the pitting behavior of stainless steels. The linear relation was observed between the logarithm of the maximum pit depth and the logarithm of the exposure year, and the slope of the line was around 0.6. The pitting resistance of stainless steels depends on the alloy index, [Cr]+2[Mo], which was derived from multi-regression analysis. Here [Cr] and [Mo] mean chromium and molybdenum concentration in mass% respectively. The same pitting behavior was observed in the specimens tested with the newly developed cyclic corrosion test. The cyclic conditions are as follows: a synthetic seawater splay (14.4ks), drying (7.2ks), and wetting (7.2ks). The maximum pit depth in the actual environment can be estimated from the results of this test.