Objective To observe effects of fluid shear stress strength on mRNA expression of ATP6V1a1 in rat polarized osteoclasts. Methods Rat polarized osteoclasts suffered 0.0(control group), 0.9, 2.9, 8.7 and 26.3 dynes/cm2 fluid shear stress for 30 min. mRNA expression of ATP6V1a1 was detected by Real - Time fluorescent quantitation PCR. Results mRNA expression of ATP6V1a1 in 0.0(control group), 0.9,2.9,8.7 and 26.3 dynes/cm2 groups was (1.14±0.06)×106, (1.62±0.09)×106, (2.28±0.13)×106, (3.24±0.18)×106, (9.16±0.53)×106 copy numbers, respectively (P