The effect of platelet‐derived growth factor (PDGF)‐AA on the inflammation in rheumatoid arthritis (RA) and osteoarthritis (OA) was investigated using cultured fibroblast‐like synoviocytes (FLS) obtained from RA and OA patients as well as control nonarthritic (NA) individuals. PDGF‐AA increased the mRNA and protein expressions of proinflammatory cytokines, interleukin (IL)‐1β and IL‐8 in RA FLS. Biological activity of IL‐1 in the culture supernatant of RA FLS was also increased by PDGF‐AA stimulation. Interestingly, PDGF‐AA synergized with tumour necrosis factor (TNF)‐α to upregulate the protein expressions of IL‐1β and IL‐8. PDGF‐induced enhancement of the IL‐1β and IL‐8 mRNA expressions was also observed in OA FLS. However, the expression of these proinflammatory cytokines in NA FLS did not change by PDGF treatment, suggesting that the inflammatory condition might have modified the biological effects of PDGF. In accordance with the enhanced expression of inflammatory cytokines, the activity of nuclear factor κB was also induced in response to PDGF‐AA in RA FLS. These results suggest that PDGF‐AA plays an important role in the progression of RA inflammation, and inhibiting PDGF activity may be useful for the effective RA treatment.