Background While fish oil (FO) has attracted great attention due to their health-enhancing properties, its potential to enhance benefits from resistance exercise training (RET) has not been fully elucidated yet. Aims The aim of this study was to investigate effects of FO administration during 12 weeks of programmed RET on muscular strength, resting metabolic rate (RMR), and systemic inflammation in healthy older adults. Methods Twenty-eight healthy older adults were randomly assigned to three experimental groups: sedentary control (CON), resistance exercise training (RET), or RET combined with FO (RET-FO). A one-repetition (1RM) of maximum muscle strength, RMR, substrate oxidation, and blood inflammatory biomarkers were assessed before and after the intervention. Statistical significance was set at p  ≤ 0.05. Results 1RM muscle strength was significantly increased in RET and RET-FO while substantially decreased in CON. RMR greatly increased in RET and RET-FO with no change in CON. RET-FO exhibited significantly increased fatty acid oxidation, but no change was found in CON and RET. Systemic interleukin 6 (IL-6) and C-reactive protein (CRP) were significantly decreased from baseline in RET-FO while no change was observed in CON and RET. Conclusion Our data indicate chronic RET reversed aging-induced loss of muscle strength and improved RMR, while FO administration combined with RET appears to enhance fat metabolism and mildly reduce some indicators of systemic inflammation.