Rofecoxib, apart from its antiinflamatory, analgesic and antipyretic activity, is a Class II drug according to the BCS and suitable for being formulated as microspheres with bovine serum albumin. In this study, rofecoxib microsphere formulations were developed and characterized. One of the prepared formulations that has a particle size of 13.48 +/- 2.11 mu m, 35.20 +/- 1.32% of encapsulation efficiency and better- sustained release (up to 18 h) was chosen for the in vivo experiments. A Level A IVIVC was evaluated between the in vitro dissolution and in vivo plasma concentration-time profile data. Linear regression analysis showed a statistically significant relationship between the in vitro dissolved percentages and in vivo absorbed percentages of the drug and the best fitted equation was described.