[en] The prior austenite grain size, bainite colony size and average grain size after intercritical quenching in A508-3 steel have been measured, and factors which have an effect on them have been discussed. The results have shown that a small amount of aluminium contained would induce serious mixed structure with fine and coarse grains in the prior austenite. Fast cooling rate would give fine bainite colony and very fine grain structure could be obtained by means of the intercritical quenching