Abstract: Objective To study the application of functional magnetic resonance imaging (fMRI) in showing the effect of simulated weightlessness on emotional stability. Methods Eight male astronaut volunteers underwent stimulated weightlessness experiments in bed for 3 weeks, followed by fMRI. Results Signifcantly activated areas were observed in bilateral mid-occipital gyrus, occipital cuneus, bilateral mid-frontal gyrus of prefrontal and bilateral thalamus, and a small activated area appeared in bilateral limbic lobe subiculum hippocampi and right amygdaloid nuclei at simulated weightlessness experiments before lying in bed. The size and signal intensity of activated brain were similar at simulated weightlessness experiments before and after lying in bed. Conclusion The effect of stimulated weightlessness is similar on emotional stability of astronaut volunteers.