Background and Objectives: Aging and malnutrition are known to influence immune functions. The aim of this study was to investigate the relationship of aging and malnutrition to innate immune functions in tube-fed bedrid- den patients. Methods and Study Design: A cross-sectional survey was performed in 71 tube-fed bedridden pa- tients aged 50-95 years (mean age±SD, 80.2±8.5 years) with serum albumin concentrations between 2.5 and 3.5 g/dL. We evaluated associations of age and nutritional variables with natural-killer cell activity, neutrophil- phagocytic activity, and neutrophil-sterilizing activity. Nutritional variables included body mass index, weight- adjusted energy intake, total lymphocyte count, and serum concentrations of albumin, transferrin, prealbumin, to- tal cholesterol, C-reactive protein, and zinc. Results: Natural-killer cell activity, neutrophil-phagocytic activity, and neutrophil-sterilizing activity were normal or increased in 67 (94%), 63 (89%), and 69 (97%) patients, re- spectively. Multiple linear regression analysis with a backward elimination method showed that natural-killer cell activity correlated negatively with aging and lymphocyte counts (p<0.01 for both) but positively with body mass index and transferrin (p<0.01 for both). Neutrophil-phagocytic and neutrophil-sterilizing activities were not asso- ciated with any variables. Conclusions: In tube-fed bedridden patients with hypo-albuminemia, natural-killer cell activity may be associated with aging, body mass index, transferrin, and lymphocyte counts.