To provide an organic wastewater treatment method capable of reducing the amount of excess sludge produced at a low cost while keeping water quality good.

The organic wastewater treatment method for treating organic wastewater using an activated sludge method has such a process that at least one kind of a compound selected from a wood vinegar liquid, sodium hydroxide, polyphenols and organic acids and metal salts thereof is added to and mixed with activated sludge taken out of an activated sludge treatment process and this activated sludge is returned to at least one of the aeration tank and flow rate adjusting tank in the activated sludge treatment process.