Primary tenocytes rapidly undergo senescence and a phenotypic drift upon in vitro monolayer culture, which limits tendon research. The Ink4a/Arf locus encodes the proteins p16Ink4a/Arf and p14ARF (p19ARF in mice) that regulate cell cycle progression and senescence. We here established an immortalized cell line using tenocytes isolated from Ink4a/Arf deficient mice (Ink4a/Arf−/−). These cells were investigated at three distinct time points, at low (2–5), intermediate (14–17) and high (35–44) passages. Wild-type cells at low passage (2–5) served as controls. Ink4a/Arf−/− tenocytes at all stages were comparable to wild-type cells regarding morphology, expression of tenogeneic genes (collagen type 1, 3 and 5, Scleraxis, Tenomodulin and Tenascin-C), and surface markers (CD29, CD44 and CD105) and form 3D tendon-like structures. Importantly, Ink4a/Arf−/− tenocytes maintained their phenotypic features and proliferation potential in culture for more than 40 passages and also following freeze–thaw cycles. In contrast, wild-type tenocytes underwent senescence starting in passage 6. These data define Ink4a/Arf−/− tenocytes as novel tool for in vitro tendon research and as valuable in vitro alternative to animal experiments.