We have investigated the effects of Notch1 knockdown and treatment with TGF-β1 on the regulation of the directional differentiation of mesenchymal stem cells (MSCs). MSCs were isolated from the femur bone of New Zealand rabbits and purified by using discontinuous gradient density centrifugation. Notch1 siRNAs were designed, synthesised and transiently transfected into these MSCs, and treated with TGF-β1. The MSCs were examined for morphology, stained with toluidine blue for proteoglycan analysis and gene and protein expression were measured with qRT-PCR and Western blotting respectively. They had an ellipse or fusiform shape and gathered in nests or swirls after being cultured for 7 days. Notch1 expression was knocked down with Notch1 siRNA (the silence rate was 47%; P < 0.001). After knockdown and TGF-β1 treatment, MSCs expressed more proteoglycan (P < 0.01), and higher levels of collagen II mRNA and protein than control cells (P < 0.001). Thus knockdown of Notch1 expression in MSCs may be useful in the treatment of intervertebral disc degeneration.