The interaction between 20(S)-protopanaxatriol (PPT) and bovine serum albumin ( BSA) was studied with fluorescence quenching technique and ultra-violet absorption spectroscopy. The results indicated that PPT led to the intrinsic fluorescence quenching of BSA through a static quenching process .The binding constants of PPT with BSA obtained with fluorescence quenching method were calculated as 0.926 3×103 (298 K), 0.618 2×103 (308 K), 0.414 4×103 L·mol-1(318 K), respectively; while the number binding sites n were close to unity. The results showed that the driving force of the interaction between PPT and BSA was hydrogen bond and Van der Waals force. The result of synchronous fluorescence spectra showed that binding of PPT with BSA could induce conformational changes in BSA, that the part of tryptophan became more closely. According to Fster fluorescence resonance energy transfer theory, the binding distance r and energy-transfer efficiency E were respectively 26.2 nm and 0.32.