Human physical and cognitive functions decline with age, increasing the likelihood of reduced independence in older adults. Nuts are nutrient-dense, and research has shown that regular nut consumers have better functional capacity (1), but evidence from intervention trials is lacking. Therefore, this study aimed to investigate if daily peanut butter (PB) supplementation over 6 months can lead to better physical and cognitive function in community-dwelling older adults. This was a 6-month randomised, controlled, parallel-arm clinical trial that included 120 adults (clinical trial registration: ANZCTR12622001291774). Inclusion criteria included: aged 65 years and older, high-risk for falls, BMI 18-35 kgm-2, generally healthy or with metabolic diseases managed through lifestyle or medication (except insulin). Participants were excluded if they were taking oral nutrition supplements or undertaking structured exercise training. Participants were randomly allocated into the Control (no intervention (CL), n = 60) or nut (43g/d PB, n = 60) group. Pre-portioned PB was provided for the nut group, and compliance was assessed as unconsumed and returned PB cups. Assessments were conducted at baseline and 6-months, and included: i) physical function (4-meter gait speed (primary outcome), standing balance test, 4-square step test, 5-time and 30-second sit-to-stand (STS) tests, timed up-and-go tests; ii) handgrip and isometric knee-extension strength tests; iii) anthropometry and body composition (weight, BMI, total lean and fat mass, appendicular lean mass); iv) cognitive function (Montreal Cognitive Assessment (MoCA), trail-making tests A and B (TMT-A, TMT-B)); and v) dietary intake (3-day food records). Missing data was handled using multiple imputations. Linear regression models, adjusting for age, sex, baseline value of the dependent variable, BMI, physical activity and diet quality, were performed to determine intention-to-treat intervention effects. At baseline, 70% were females, and age = 76.1 ± 4.6 years, BMI = 27.5 ± 4.2 kg/m². Compliance to PB intervention was 86.0 ± 13.8%. Post-intervention, the PB group had significantly higher energy (p = 0.001), protein (g/d, p = 0.040) and fat (%E, p < 0.001), and lower carbohydrate (%E, p = 0.002) intake. Of all physical function outcomes, only 5-time STS significantly improved more in PB than CL (mean difference for change, -1.2 seconds (95%CI: -2.1, -0.4)). No significant between-group differences in changes in muscle strength, weight, BMI, lean mass, or appendicular lean mass were observed. In terms of cognitive function, improvements in MoCA scores and TMT-B in PB approached statistical significance (p = 0.085 and p = 0.053 respectively) compared with CL, nut not TMT-A. In conclusion, PB supplementation was feasible and resulted in an improvement in 5-time STS and some measures of cognition, but not other measures of strength or body composition. PB also improved protein intake without increasing weight gain.