This study was designed to reveal the characteristics of the strains degrading formaldehyde isolated from mud of waste water. A strain H-5 showed the highest ability of formaldehyde biodegradation among isolated strains. According to identification, the strain H-5 was ascribed to be Peudomonas putida H-5. The optimal conditions of Peudomonas putida H-5 were $30^{circ}C$ and pH 7.0. The highest level of formaldehyde degradation was demonstrated at the concentration of 0.02~0.04% in a glucose containing medium. Formaldehyde biodegradation by Peudomonas putida H-5 indicated that this reaction was converted to the methanol and formic acid. However, methanol and formic acid did not show any effect on the growth of viable cells.