Mutation rate of M₂ plants that were treated with three types of double treatments of chemical mutagens(1.5mol NaN₂ + 0.75mol MNH, 0.75mol MNH + 0.75mol MNH and 0.5mol MNH + 0.5mol MNH) were estimated on the rate of chlorophyll mutant, changes of isozyme loci ; esterase (Est), glutamate oxaloacetate transaminase (GOT ; AAT) and leucyl aminopeptydase(LAP ; AMP). Rate of chlorophyll mutants (3.3% = no. of seedling carrying mutant / all number of M₂ seedlings x 100) and rate of esterase isozyme loci mutants(3.5% = no. of plant carrying mutant / all number of M₂ plant) in Dema were higher than one of Sacheon 6, but no significant differences in GOT, LAP. Among isozymes, most of mutants in M₂ plant of two varieties were found in esterase (73% of total mutants were occurred in esterase loci). Although many of null bands were found in GOT 3, these were not repeatable and no real mutants. It might be due to qualities of starch, amount of extract buffer and degradation of isozyme during electrophoresis and staining.