Valeriana hardwickii ("'Nu lang") has been used in folk medicine Vietnam for treatment of anxiety, sleep disorders, etc. The acute toxicity of dichloromethane, 45 percent ethanol and water extracts was orally carried out in mice and the anxiolytic, tranquilizing effect of above extracts were evaluated by forced swimming test (FST), open field test (OFT) and light dark test (LDT) in mice. The results of this study showed that the extracts exerted no acute toxicity at the tested dose (dichloromethane extract 5000 mg/kg, 45 percent ethanol extract 11900 mg/kg, water extract 14640 mg/kg). No changes were observed on mice organs after 14 days. The dichloromethane extract (250 mg/kg and 500 mg/kg), 45 percent ethanol extract (595 mg/kg and 1190 mg/kg) and water extract (732 mg/kg and 1464 mg/kg) reduces the immobile time in the FST and show anti-depressant effect and dichloromethane extract (500 mg/kg) shows the strongest effect. There is no significant difference from that offluoxetine (20 mg/kg PO). The 45 percent ethanol extract (595 mg/kg, 1190 mg/kg), and the water extract (732 mg/kg, 1464 mg/kg) increase number of squares crossed, number of rearing and time spent at the center square in OFT, and time spent in the light compartment and number of transitions in LDT. Oichloromethane extract at dose of 250 mg/kg increases time spent in the light compartment and number of transitions in LDT. Oichloromethane extract at dose of 500 mg/kg increases the number of transitions in LDT. The results revealed that the extract possess anxiolytic and tranquilizing effects in mice.