Background Literature about life satisfaction in rural senior older adults is scarce. The aim of this research was to examine the relationships among mental health, social capital and life satisfaction in rural senior older adults. Methods This was a cross-sectional study. From July to October 2017, 245 senior older adults from 14 villages of Jinhua City in China were recruited. The Satisfaction with Life Scale (SWLS), the Chinese Version of the 12-item General Health Questionnaire (GHQ-12), the Social Capital Questionnaire (SCQ) and a self-designed questionnaire was administered to the participants. Structural equation modelling was implemented to analyse the relationships between mental health, social capital and life satisfaction in rural senior older adults. Results The structural equation model was fitting adequately (χ2/df = 1.785, P < 0.001; RMSEA = 0.059; CFI = 0.963). Life satisfaction was positively affected by income (β = 0.243, P = 0.01). Likewise, community canteen services improved life satisfaction (β = 0.288, P = 0.001). Social capital had direct positive prediction on life satisfaction (β = 0.342, P = 0.003) and indirectly improved life satisfaction through mental health (β =0.183, P = 0.007). Life satisfaction was impaired by poor mental health among senior older adults (β = − 0.395, P < 0.026). Conclusions Life satisfaction among rural senior older adults is a multifaceted well-being construct affected by income, community canteen services, social capital and mental health. The presented model highlights the positive effect of income, community canteen services, social capital and mental health. Appropriate home-based aged care, programs and policies are needed.