Secoisolariciresinol (SECO) is a natural lignan-type phytoestrogen constituent mainly found in flaxseed. It can be metabolized in vivo to mammalian lignans of enterodiol and enterolactone, which have been proven to be effective in relieving menopausal syndrome. Depression is one of the most common symptoms of menopausal syndrome, and is currently treated with estrogen replacement and antidepressant therapy. However, due to the serious side-effects of such agents, there are urgent needs for safer and more tolerable treatments. In this paper, using two classical depression models, the forced swimming test and the tail suspension test, we report the antidepressant effect of SECO on ovariectomized (OVX) mice by intragastric administration for 14 consecutive days at doses of 5, 10 and 20 mg/kg. The results showed that SECO (10 mg/kg) treatment could significantly reduce the duration of immobility of OVX mice in these two models compared with the control group (OVX mice + vehicle), which was similar to the positive control imipramine. In addition, SECO treatment could substantially increase brain monoamine (norepinephrine and dopamine) levels in OVX mice. The present studies showed that SECO can reverse depressive-like behavior and exhibit monoamine-enhancing effects.