Objectives To investigate the associations of n-3 fatty acid intake with handgrip strength and muscle mass indices in older adults. A secondary aim was to investigate whether these associations differed by physical activity status. Research methods & procedures A cross-sectional study included 53,170 participants aged 60 years and over from the UK biobank (25,324 men and 27,846 women). The primary outcomes were grip strength index and muscle mass index, the predictor variable was n-3 fatty acid intake and the covariates were age, ethnicity, Townsend deprivation index, physical activity, multimorbidity count, total energy intake, body fat percentage and the month of assessment. Multivariable linear regression analyses were performed across 5 models. Model 1 was unadjusted; model 2 adjusted for age, ethnicity, deprivation index and month of assessment; model 3 adjusted as in model 2 plus total energy intake; model 4 as in model 2 plus multimorbidity count; and model 5 as in model 4 plus body fat percentage. Results In model 5, higher n-3 fatty acid intake was positively associated with the grip strength index in women. For each additional gram of n-3 fatty acid consumed per day, there was an increase of 0.03 kg/m2 (95% CI: 0.00 to 0.06 kg/m2) in active women and 0.04 kg/m2 (95% CI: 0.00 to 0.07 kg/m2) in inactive women. However, no significant associations were observed in men, whether active (p = 0.405) or inactive (p = 0.323). Additionally, no significant associations were found between n-3 fatty acid intake and muscle mass index in either active (p = 0.858) or inactive (p = 0.250) men, or in active (p = 0.909) or inactive (p = 0.187) women. Conclusion Although n-3 fatty acid intake was associated with grip strength index in older women, regardless of their activity status, the magnitude of this association was very small and unlikely to be clinically relevant. Additionally, n-3 fatty acid was not associated with muscle mass index.