An object of the present invention is to provide a method for efficiently degrading a biodegradable resin. In particular, the present invention relates to a method for degrading a biodegradable resin, the method comprising degrading the biodegradable resin in a buffer solution containing a biodegradable resin-degrading enzyme having an optimum pH of 7.5 or higher, wherein no anion derived from a buffer component is present on one side of an equilibrium equation of buffering of the buffer solution, and a pH of the buffer solution is adjusted within a pH range which gives conditions for shifting the equilibrium towards the side on which no anion is present. Further, the present invention relates to a method for degrading a biodegradable resin, the method comprising degrading the biodegradable resin in an enzymatic reaction liquid containing a biodegradable resin-degrading enzyme having an optimum concentration, wherein the degradation is conducted in a reaction liquid having an enzyme concentration which gives a biodegradable resin degradation ratio of 60% or higher, where a biodegradable resin degradation ratio at said optimum concentration is referred to as 100%.