Objective To explore the role of mechanical stimulation in synovium under different pathological conditions through studying the effects of cyclic mechanical stretch on the expression of bone morphogenetic protein 2 (BMP-2) in rheumatoid arthritis (RA) and osteoarthritis (OA) fibroblast-like synoviocytes (FLS). Method 6% and 0.5 Hz stretch generated by Flex cell 4000 tension systems was applied on normal, RA and OA FLS of human knee joint source under normal and inflammatory conditions for 2 h or 6 h, respectively. Results Cyclic mechanical stretch of 6%, 0.5 Hz had no significant effects on the expression of BMP-2 in normal, RA and OA FLS at 2 h, while in RA FLS it increased significantly at 6 h. Inflammatory cytokines (IL-1β) didn’t influence normal FLS at 2 h, but made BMP-2 mRNA significantly increased at 6 h. IL-1β increased BMP-2 mRNA of RA FLS significantly both at 2 h and 6 h. IL-1β increased BMP-2 mRNA of OA FLS significantly only at 2 h, but had no significant effect at 6 h. The co-effect of IL-1β and cyclic mechanical stretch induced the ascension of BMP-2 expression significantly in normal and RA FLS at 2 h, and in normal, RA and OA FLS at 6 h. Conclusions Response of BMP-2 mRNA to mechanic stimulation and IL-1β in normal, RA and OA FLS were different. Inflammation may play a more important role than mechanical stimulation in the pathogenesis of RA and OA. Synergetic effect in inflammation and mechanical stimulation were found in OA FLS at 6 h, which reveals that they may co-act in the occurrence and development of OA.