Thin sections in castings solidify faster than thick sections. Solidification rates increase because of an increase in heat transfer from molten meltals to molds through these solidified thin sections. The cooling fin effect in pure zinc casting was studied about the solidification time, superheat, and fin size by adopting the pourout test. The following results could be obtained from the study: (1) The fin effect could be represented by the effective cooling surface area (A_f/S) increased. (2) The fin effect could be obtained as functions of solidification time, superheat, and fin size.