To provide a method for treating an organic waste by using a mixed microorganism containing a microorganism which has not hitherto been known to have an organic waste degradation ability, and to provide an organic waste treating agent for use therein.

In this method for treating an organic waste, the organic waste is treated with a mixed microorganism containing at least one microorganism belonging to the genus Providencia or the genus Proteus, preferably further containing a microorganism belonging to lactobacillus and/or a microorganism belonging to the genus Pseudomonas.