Osteocytes, which comprise over 90% of all bone cells, communicate with osteoblasts and osteoclasts to regulate each other's physiological function via dendrites, suggesting that dendrite elongation plays a vital role for bone regeneration. We examined the effect of semaphorin 3A (SEMA3A) on dendritic processes of an osteocyte cell line, since in previous work we found it to be essential for promoting osteoblast differentiation. Dendrite length was analyzed by Cellomics Array Scan VTI quantitatively in osteocyte-like cell line, MLO-Y4 cells. We performed cell proliferation assay. Gene and protein expression was examined by real-time reverse-transcriptase polymerase chain reaction and western blotting, respectively. Both total and average dendrite length were significantly increased in MLO-Y4 cells stimulated with SEMA3A compared to control. E11 protein was up-regulated upon SEMA3A stimulation. Moreover, cyclin-dependent kinase 6 (CDK6) was down-regulated in a time-dependent manner. Taken together, these results suggest that SEMA3A regulates dendrites of osteocytes in association with down-regulation of CDK6. SEMA3A may be a promising drug to apply for bone tissue engineering.