The present disclosure relates to propiconazole resistant mutants of Chlorella species having Accession No. CCAP 211/134. The propiconazole resistant mutants of Chlorella species has increased tolerance to propiconazole and has increased tolerance to abiotic stress. 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, has increased tolerance to temperature stress, and hence can be used for large scale production of algal biomass.