Depression is a common mental disorder and mainly characterized by persistent sadness and a lack of interest or pleasure in previously rewarding or enjoyable activities. Despair is also a common symptom of depression, and the forced swim and tail suspension tests are widely used to measure this behavior in rodents, but the results from these tests can include the effects on stress resistance in addition to depressive-like states. Reduced motivation is an important marker of psychiatric disorders, including depression, and thus we have previously developed the female encounter test, a novel and simple procedure for assessing reward-seeking behavior in adult male mice. Importantly, female mice should be considered in the development of animal models of depression and assessment of mouse behaviors since the lifetime prevalence of a major depressive disorder in women is almost twice that in men, and around one in seven women can develop postpartum depression. In this review, we summarized our recent research on the male encounter test for assessing motivation in adult female mice and introduced new topics on animal models and therapeutic drugs for postpartum depression.