Novel biodegradable aliphatic poly(ester-urethane)s (PEUs) based on polycaprolactone diol (PCL) and methoxypolyethyleneglycol grafted onto trimethylol propane (mPEG,-g-TMP) were synthesized by solution polymerization technique and characterized using a variety of techniques. Microsphere ranging in size from 7 to 25 mu m were prepared by the solvent evaporation technique and loaded with repaglinide up to 71 to 96%. Increasing molar ratios of mPEG-g-TMP propane with respect to polycaprolactone diol gave increase in particle size along with increase in % encapsulation efficiency. Surface morphology and spherical nature of the microsphres were confirmed by scanning electron microscopy (SEM). The release of repaglinide varied, depending upon the molar ratios of mPEG-g-TMP moieties with respect to PCL. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 251-257, 2009