The present invention provides a biodegradable drug delivery composition comprising: (i) a mixture of at least three different block copolymers, wherein each block copolymer is: (a) a biodegradable triblock copolymer having the formula: Av-Bw-Ax wherein A is a polyester and B is polyethylene glycol and v and x are the number of repeat units from 1 to 3,000 and w is the number of repeat units from 3 to 300 and v=x or v≠x； or (b) a biodegradable diblock copolymer having the formula: Cy-Az wherein A is a polyester and C is an end-capped polyethylene glycol and y and z are the number of repeat units with y=2 to 250 and z=1 to 3,000； and wherein the mixture comprises at least one (a) and at least one (b)； and the weight ratio between (a) and (b) is 1:19 to 5:1； and (ii) at least one pharmaceutically active ingredient.
