The aim of the present study was to investigate the effects of phosphorylated osteopontin (p-OPN) on apoptosis and pro-inflammatory cytokine expression in human knee osteoarthritis (OA) chondrocytes. Human knee OA chondrocytes obtained from patients who underwent total knee arthroplasty were treated with p-OPN, OPN or buffer. Reverse transcription quantitative-polymerase chain reaction (RT-qPCR) and western blot analysis were used to assess the expression levels of proinflammatory factors, including interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6 and nuclear factor (NF)-κB. Apoptosis of human knee OA chondrocytes was detected by Annexin V-fluorescein isothiocyanate/propidium iodide flow cytometry. Compared with the controls, chondrocytes treated with OPN exhibited higher mRNA and protein expression levels of proinflammatory factors (IL-1β, TNF-α, IL-6 and NF-κB), and a higher percentage of apoptotic chondrocytes. Furthermore, chondrocytes treated with p-OPN exhibited the highest mRNA and protein expression levels of proinflammatory factors (IL-1β, TNF-α, IL-6, NF-κB) and the highest percentage of apoptotic chondrocytes. p-OPN induces chondrocyte apoptosis and proinflammatory factor release, which suggests that p-OPN may contribute to OA pathogenesis, and inhibition of p-OPN may provide a novel effective strategy to slow or halt OA progression.