Happiness is a subjective experience that is an ultimate goal for humans. Psychological studies have shown that subjective happiness can be measured reliably. However, the structural and functional neural substrates of subjective happiness remain unclear. To investigate this issue, first, we used structural magnetic resonance imaging (MRI) and questionnaires that assessed subjective happiness. We found a positive relationship between gray matter volume in the right precuneus and the subjective happiness scores. Next, we analyzed resting-state functional MRI. Reduced low-frequency fluctuations in the right precuneus were associated with higher subjective happiness scores. Furthermore, functional and effective connectivity of the right precuneus with the right amygdala were positively associated with subjective happiness scores. These results indicate that the structure, activity, and connectivity of the precuneus play an important role in implementing subjective happiness. The findings, together with other evidence on the information-processing functions of these brain regions, suggest that subjective happiness is associated with a reduction in self-referential mental processes, which is well integrated with emotional processing.