Depression is a psychosomatic disorder. The rising incidence rate of depression in recent years is placing a heavy economic burden on societies around the world. Morinda officinalis oligosaccharides ( MOOs) are active substances extracted from the Chinese herb Morinda officinalis that can soothe depression and calm the mind, tonify the kidneys, and benefit the intellect, as well as improve cognitive disorders in patients to a certain extent. On the basis of the hypothesised pathological mechanism of depression, this study explains the link between MOOs and depression by reviewing existing studies. We propose that MOOs can improve depression through mechanisms that regulate the levels of monoamine neurotransmitters, enhance neuroplasticity, regulate the function of the HPA axis and levels of cytokines, and influence gut microbiota. This paper provides new ideas for research on the antidepressant effects of MOOs.