Auxotrophic mutants and phenol-degrading defective mutants were separately isolated in a phenolutilizing strain of Candida tropicalis M4, and were hybridized through protoplast fusion. Some protoplast fusants with phenol-degrading ability were obtained and were very stable. Two of the fusants exhibited slightly higher rates of growth than did the wild strain when the cells were grown on phenol medium, and they possessed about 1.9 and 2.2 times respectively higher phenol hydroxylase activity than the wild strain.