Membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome (NS) in adults, which can be divided into the primary and secondary types. The secondary MN accounts for about 1/3 of the total MN. Among the secondary MN, the tumors- and drugs-related MN is of significance and controversial, which need to be paid attention to and screened clinically. Although it is hard to differentiate accurately between tumors-related MN and IMN complicated with tumors, the following should be noted: the existence of tumors should not be ignored in middle-elderly patients with MN, which should be screened carefully; if the tumor is found, indexes of early renal damage should be measured for proper diagnosis and necessary interfering treatment; and for nephrotic syndrome in the middle-elderly patients with MN, before and during the application of corticosteroids and immunosuppressants, the possibility of tumors should also be ruled out. For MN patients who have a history of exposure to mercury, attention should be paid to exclude the mercury poisoning-related MN.