Objective To define risk factors of nosocomical pneumonia (NP) in elderly in-patients. Methods Two hundred elderly in-patients were selected in the Geriatric Department of West China Hospital from January 1999 to June 2002. Among them, 100 patients developed NP during their hospital days and the others didn’t have the episodes of NP at the same time. The following factors were analyzed: sex, age, multiple underline diseases and their severity, smoking, activity of daily life, conscious status, aspiration, nasogastrial intubations, antibiotics use and hospitalization. SPSS 10.0 was used for Logistic regression analysis to determine the factors significantly associated with the development of NP. Results The following factors were significantly associated with the development of NP in the logistic regression analysis: aspiration [OR 28.452, 95%CI (3.793 to 213.447)],multiple diseases [OR 17.157, 95%CI (2.734 to 107.651)], multiple antibiotics use [OR 6.396, 95%CI (1.861 to 21.980)], smoking [OR 1.774, 95%CI (1.211 to 2.600)] and prolonged hospitalization [OR 1.134, 95%CI (1.081 to 1.189)]. Conclusions Aspiration, multiple diseases, multiple antitiotics use, smoking and prolonged hospitalization are closely related to NP in elderly in-patients. Cautionary medical measures and shortening hospitalization were the key factors to decrease the incidence of NP for the patients in Geriatric Department.