Objective To identify the differentially expressed proteins and clarify the major proteins involved in the molecular mechanism of osteoblasts under mechanical strain loading. Method Saos2 osteoblastic cells were subjected to 12% elongation for 24 hours by using Flexcell strain loading system. Proteins extracted from Saos2 cells were separated by twodimensional electrophoresis (2DE). Differential expressed protein spots among groups were submitted to matrixassisted laser desorption/ionization time of flight mass spectrometer (MALDITOF MS) assay and peptide mass fingerprinting (PMF) identification. The SwissProt and NCBI databases were used to obtain further information about proteins identified. Results Saos2 stimulated by mechanical strain showed a significant difference in 2DE system compared with the control group. A total of (1031±41) or (928±25) protein spots were resolved by 2DE of controls or experimental groups extractions respectively. 17 significant up  regulated proteins were identified. These associated proteins fell into 6 groups, including stress reaction, energy metabolism, cell proliferation, reconstruction of cytoskeleton, signaling and osteogenesis. Conclusions The Saos2 can express differential proteins stimulated by mechanical strains and these proteins may play an important role in molecular mechanism of osteoblasts under mechanical strain loading.