Abstract: Objective To investigate the expression level of Notch1 gene in patients with lymphoid malignancies. Methods Real-time PCR with SYBR GreenⅠ technique was used to detect Notch1 gene expression level in peripheral blood mononuclear cells of 43 patients with lymphoid malignancies, including 7 cases with T-ALL, 6 cases with T-NHL, 9 cases with B-ALL, 5 cases with B-CLL, 16 cases with B-NHL and 20 healthy individuals. β2-microglobulin gene (β₂M) was used as an endogenous control. Relative level of Notch1 gene expression were analysed by the 2^-ΔCt×100% method. Results The expression level of Notch1 in both T-cell lymphoid malignancies group (Median: 0.897%) and B-cell lymphoid malignancies group (Median: 0.726%) was significant higher than that in the healthy control (Median: 0.288%) (P<0.01, P<0.01). However, the expression level of Notch1 was different in the five types of lymphoid malignancies. The highest level was observed in the B-CLL group, secondary in the T-NHL group, the lowest in the B-NHL group. Conclusions The abnormal expression of Notch1 might played an important role in the pathogenesis of lymphoid malignancies. The result provided the preliminary basis for targeting the Notch1 pathways.