The objectives of this study were (l) to screen out active proline-specific peptidases from Lactobacillus casei subspecies, (2) to study growth kinetic and enzyme production from enriched medium (MRS) and cheese whey medium, (3) to purify and characterize two active proline-specific enzymes, and (4) to investigate the action of purified enzyme on bitter tryptic digests of $ beta$-casein as well as bitter enzyme-modified cheese. Lactobacillus casei subsp. casei LLG and Lactobacillus casei subsp. rhamnosus S93 were examined for extra- and intra-cellular proline-specific peptidase activities. Both strains showed strong activity for x-prolyl dipeptidyl peptidase and proline iminopeptidase but had weak activities for prolidase, prolinase, and post proline endopeptidase. Histochemical staining of crude enzyme extract from Lactobacillus casei ssp. casei LLG with different substrates revealed a distinct protein band for x-prolyl dipeptidyl peptidase as well as for proline iminopeptidase. The growth kinetics showed that the intracellular proline-specific peptidases increased gradually at the beginning of the exponential phase and reached a maximum at the beginning of stationary phase.