Sports-related tendinopathy is commonly treated with nonsteroidal anti-inflammatory drugs including cyclooxygenase-2 inhibitor. Tendon healing requires migration of tendon cells to the repair site, followed by proliferation and synthesis of collagen. This study was designed to determine the effects of COX-2 inhibitor (celecoxib) on the migration, proliferation, and types I and III collagen expression of tendon cells intrinsic to rat Achilles tendon. Using cultured tendon cells, cell migration and proliferation were evaluated by transwell filter migration assay and by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay, respectively. The mRNA expression of alpha1(I) procollagen and alpha1(III) procollagen were determined by reverse transcription-polymerase chain reaction (RT-PCR). The protein expression of types I and III collagen were determined by immunocytochemistry. Dose-dependent celecoxib inhibition was demonstrated for migration of tendon cells through the transwell filter migration assay (p=0.002). Dose-dependent celecoxib inhibition of tendon cell proliferation also was demonstrated by MTT assay (p=0.004). However, both RT-PCR and immunocytochemical staining revealed that mRNA and protein expression of types I and III collagen remained constant after celecoxib treatment. In conclusion, celecoxib inhibits tendon cell migration and proliferation. However, the expression of types I and III collagen remained unchanged.