The effect of film thickness from 33 to 211 mum on the degradation of pigmented long oil alkyd resin paint film coated on a steel plate in a 3% NaCl solution was investigated by use of a scanning acoustic microscope (SAM) and a nanoindentation tester. The growth speed and progress pattern of blisters observed by SAM were classified as three types. In the case of a type A blister, at first a lower Young's modulus (E) area generated partially, a lot of fine blisters initiated in the area at the initial stage that connected with each other and became large. In the case of a type B blister, the initiation time of blistering was long, and the blisters grew rapidly and became large once they appeared. In the case of a type C blister, the initiation time of blistering was long, and blisters grew slowly if they appeared. The blister of 33 mm film showed type A, the blister of 47 mm film showed type A or type B, the blisters of 119, 154, and 211 mm film showed type B and/or type C blistering. Furthermore, type A initiated before the immersion time of maximum E peak value (T-EP), and type B and type C initiated after T-EP. (C) 2003 The Electrochemical Society.