The present disclosure relates to propiconazole resistant mutants of Chlorella sp. having Accession No. CCAP 211/133. The propiconazole resistant mutants of Chlorella species have increased tolerance to propiconazole. The present disclosure further provides a method for preparing the propiconazole resistant mutants of Chlorella species. The propiconazole resistant mutants of Chlorella species can selectively grow in the presence of propiconazole, and hence can be used for large scale production of algal biomass.