In the past few decades, the number of bed-ridden elderly patients has been increasing. This group of patients is frequently fed with a liquid formula diet. The aim of this study was to evaluate the usefulness of a liquid formula diet containing dietary fiber (DF) for elderly bed-ridden patients. Eighteen elderly, bed-ridden patients were given L-3 Fiber, a DF-containing liquid formula diet (DF-LFD), for 4 weeks, while a number of parameters were monitored, including serum levels of total cholesterol, triglyceride, total protein, creatinine, uric acid, glucose, sodium, potassium, and calcium, urine protein/sugar, and defecation frequency. Total protein, albumin and total cholesterol significantly increased following the administration of the DF-LFD, associated with an average increase in body weight of 1.94 kg (5.0%). Defecation frequency significantly increased one week after DF-LFD administration was started, but this effect was transient. Although a few patients complained of nausea, vomiting or abdominal pain, no severe side effects were seen. In conclusion, DF-LFD supplementation appears to be beneficial for elderly bed-ridden patients, and can increase nutritional-related parameters, such as body weight, total protein, albumin and total cholesterol, without severe side effects.