We investigated the refolding of protein in inclusion bodies using reversed micelles formed by aerosol OT (AOT). RNase A was overexpressed in E. coli and used to prepare inclusion bodies of RNase A, which were then subjected to protein refolding by the AOT/isooctane reversed micellar system. The RNase A was renatured in reversed micelles, and the refolding yield reached 100% in 18 h. The addition of cold acetone to the reversed micellar solution allowed the recovery of the renatured RNase A without any loss of its activity. In the reversed micellar refolding system, the refolding conditions for inclusion bodies agreed with those for wild-type RNase A artificially denatured with a denaturant. This result indicates that the refolding mechanism of the inclusion bodies is similar to that of the denatured wild-type RNase A. A dilution method for refolding of the inclusion bodies caused the re-aggregation of RNase A, and only 40% of the native activity was regained. Reversed micelles effectively promoted the refolding of RNase A from its inclusion body, suggesting that a reversed micellar protein refolding method can yield a higher rate of renaturation than the conventional dilution method.