In this study the reverse micellar extraction of alpha-chymotrypsin using bis(2,4,4- trimethylpentyl) sodium dithiophosphinate as the surfactant has been investigated. Experiments were performed to determine the effects of pH and salt concentration on the reverse micellar extraction and backward extraction of alpha-chymotrypsin in isooctane/decanol mixtures. The results showed that both pH and salt concentration influence the reverse micellar extraction of alpha-chymotrypsin, The pH affects the extraction of the protein through changing the sign and number of the charges carried by protein molecules and thereby affects their interactions with the charged head groups of the surfactant molecules. It was found that at high pH values the hydrogen ions compete with positively charged protein molecules and exchange with the counterions of the surfactant molecules, and as a result destroy the reverse micelles. This effect was exploited for the backward extraction of protein molecules from the reverse micellar phase. A model has been developed to correlate the experimental data of reverse micellar extraction of proteins. In the model the reverse micelles were treated as noninteractive ion-exchange sites. The activity coefficient of the protein molecules in reverse micelles was represented by the model proposed by Fitter. It has been shown that the model can correlate the experimental data obtained in this work and those reported in other studies.