Abstract： Objective To determine the expression level of deleted in liver cancer-1 (DLC-1)gene in human pituitary tumors, and assess the correlation between DLC-1 expression and clinicopathological parameters in these tumors. Methods DLC-1 and Ki-67 protein expressions were analyzed by immunohistochemistry and DLC-1 mRNA expression by quantitative RT-PCR in 84 pituitary adcnomas and 6 normal human adenohypophyses. Results Immunohistochemical results suggested that DLC-1 expression decreased and Ki-67 expression increased in the pituitary adenomas; Pearson correlation analysis showed that they were negatively correlated (r=-0.764,P=0.001).RT-PCR indicated that DLC-1 mRNA expression decreased in the pituitary adenomas; significantly decreased DLC-1 expression in invasive pituitary adenomas was noted as compared with that in non-invasive ones (P＜0.05). Conclusion Down-regulation of DLC-1 expression may contribute to the tumorigenesis of pituitary adenomas and DLC-1 can be the new target of molecular therapy.