Objective We compared clinical outcomes with a standard (Ensure) or a high-protein (Boost HP) liquid nutritional supplement for older adults recovering from hip fracture surgery in a rehabilitation hospital. Methods This randomized, double-blind, parallel-group study compared the clinical effectiveness of a standard (Ensure) with a high-protein (Boost HP) liquid nutritional supplement among patients ( n = 46) 60 y or older who recently underwent surgical repair of a hip fracture. Patients were encouraged to drink at least two 8-oz cans (17.8 g/d protein for Ensure versus 30 g/d protein for Boost HP) per day for 28 d. Study measurements included change in Functional Independence Measure between rehabilitation admission and discharge, length of rehabilitation stay, laboratory measures (i.e., serum albumin, prealbumin, and C-reactive protein), physical activity energy expenditure by 7-d triaxial accelerometry, and dietary intake by three random, telephonic, 24-h dietary recalls. Results There were no significant group differences with respect to age, sex, acute hospital days, hip fracture assessment parameters, or surgical treatment. Consumption of supplement (260 oz/28 d of Ensure versus 239 oz/28 d of Boost HP) was comparable. There were no differences in complication or adverse event rates during the study. The Boost HP group consumed more protein than the Ensure group (63 versus 50 g, P < 0.048) and had a greater improvement in serum albumin over the 28-d supplementation period (+0.7 versus +0.2 g/dL, P < 0.019). The Boost HP group also consumed more fiber (12 versus 8 g), calcium (821 versus 639 mg), vitamin K (66 versus 45 μg), and phosphorus (1035 versus 833 mg) than did the Ensure group. Rehabilitation length of stay was shorter in the Boost HP than in the Ensure group, although this trend did not reach statistical significance (23 versus 28 d, P = 0.27). Outcome differences were not detected in the Functional Independence Measure. Conclusions Supplementation was well tolerated in this population and contributed significantly to total dietary intake. Consumption of a high-protein liquid nutritional supplement may offer some benefits by improving visceral protein status.