The present invention provides a method for obtaining organic solvent resistant microorganisms which comprises subjecting a microbial parent strain to mutagenesis and then to selective cultivation in the presence of 0.1% to 10% by volume (v/v) of concentrations of a toxic organic solvent, and the organic solvent resistant microorganisms obtainable by the method. In addition according to the present invention, a microorganism which is natively hydrophilic and has useful functions but does not show resistance to organic solvents and can not express the useful functions in the organic solvents may be converted into a microorganism capable of growing in the presence of such toxic organic solvents and expressing the useful functions that the hydrophilic parent strain bears natively. Also a bio-desulfurization bacterium mutant capable of decomposing hardly removable organic sulfur compounds under microaerobic conditions in the presence of organic solvents may be obtained by the use of a bacterium belonging to the genus and species Pseudomonas putida as the parent strain. Furthermore, the specific strains mutated from the parent strain are Pseudomonas putida No. 69-1 (FERM BP-4519), Pseudomonas putida No. 69-2 (FERM BP-4520) and Pseudomonas putida No. 69-3 (FERM BP-4521).