Objective To observe and compare the depression-like and anxiety-like behaviors in mice of different ages. Methods Twenty-seven male C57BL/ 6 mice were divided into three groups according to age: young group ( 3 months, n = 9), middle-aged group (10 months, n = 9) and old group (18 months, n = 9). The tail suspension test, forced swimming test, elevated plus maze test, open field test, and sugar preference test were used to detect depression-like and anxiety-like behaviors. Liquid Chromatography with tandem mass spectrometry was used to detect 5-hydroxytryptamine (5- HT) levels in the serum of mice. Results The immobility time of middle-aged mice was longer than that of old mice in tail suspension test( P < 0. 05); the immobility time of forced swimming decreased from young to middle-aged mice ( P < 0. 001) and from middle-aged to old mice (P< 0. 01). The sucrose preference of middle-aged mice was higher than that of old mice at 12 hours (P< 0. 05); the sugar preference rate of young mice was higher than that of old mice at 12, 36, 48, and 60 hours (P< 0. 05). The time spent in the open arms by old mice was longer than that of middle-aged and young mice (P< 0. 05) and the probe number of young mice was greater than that of middle-aged mice (P< 0. 01). The total distance travelled in the open field by young mice was longer than that of old mice (P< 0. 05). The concentration of 5-HT in the serum of old, middle-aged, and young mice showed a decreasing trend. The concentration of serum 5-HT in young mice was significantly lower than that in middle-aged (P< 0. 05) and old mice (P< 0. 01). Conclusions The younger the mice, the more likely they were to exhibit depression- and anxiety-like behaviors under the same stress stimulations, and to have a lower level of 5-HT in their serum.