Enantioselective quenching of the room-temperature phosphorescence (RTP) lifetime of proteins was demonstrated due to the effects of various external chiral quenching agents. In the absence of quenchers, the RTP lifetimes for bovine serum albumin (BSA) and human serum albumin (HSA) were found to be 5.0 +/- 0.2 and 4.0 +/- 0.1 ms, respectively. The addition of various chiral quenchers (three pairs of binaphthols and two pairs of beta-blockers) into the deoxygenated sample solutions containing BSA and HSA reduced their RTP lifetimes significantly, i.e., from ca. 4-5 ms (in the absence) to an average lifetime of ca. 1-2 ms (in the presence) of the chiral quenchers. For the R and S enantiomers examined, marked differences in RTP lifetimes were observed, i.e., ranging from ca. 20-29% for the binaphthols to ca.14-16% for the beta-blockers. Such findings could lead to a better understanding of the relationship between chirality, dynamics/conformational changes, and biological functions of proteins.