Patients with obstructive jaundice have a high susceptibility to infection in the process of treatment and the reason for this is not fully understood. It was postulated that it may bear some relations to abnormalities of immune function. In this article, 28 cases of obstructive jaundice were selected to investigate alternation of monocyte immune function with the purpose of exploring mechanism of high susceptibility to infection from the perspective of immunology. The results showed that interleukin 1 production by monocytes significantly decreased and prostaglandin E2 increased, HLA-DR expression of monocytes was remarkably depressed. HLA-DR expression of monocytes was further decreased with recovery slower than non-jaundiced patients after operation. All this may be responsible for high susceptibility to infection in the process of treatment of obstructive jaundice.