Phonon dynamics in Bi, Bi 2Se 2, and Cu xBi 2Se 3 (x = 0, 0.1, 0.125) single crystals was investigated using femtosecond pump-probe spectroscopy. Two damped oscillations in measured transient reflectivity changes were observed, respectively, attributed to coherent optical and acoustic phonons. The frequency shift of the phonon modes in Bi-rich Bi 2Se 2 crystals indicates the intercalation of the additional Bi atoms into the Bi 2Se 3 matrix and formation of the Bi 2 layer between the quintuple layers (QLs). The deformation of QLs in Cu xBi 2Se 3 crystals was also found. These phonon dynamics results suggest that Cu atoms in Cu xBi 2Se 3 crystals are predominantly intercalated between pair of QLs.