Gelsemium sempervirens is used in homeopathy for treating patients with anxiety related symptoms, however there have been few experimental studies evaluating its pharmacological activity. We have investigated the effects of homeopathic doses of G. sempervirens on mice, using validated behavioral models. Centesimal (CH) dilutions/dynamizations of G. sempervirens, the reference drug diazepam (1 mg/kg body weight) or a placebo (solvent vehicle) were intraperitoneally delivered to groups of mice of CD1 strain during 8 days, then the effects were assessed by the Light-Dark (LD) choice test and by the Open-Field (OF) exploration test, in a fully blind manner. In the LD test, the mean time spent in the illuminated area by control and placebo-treated animals was 15.98%, for mice treated with diazepam it increased to 19.91% (P = .047), while with G. sempervirens 5 CH it was 18.11% (P = .341, non-significant). The number of transitions between the two compartments increased with diazepam from 6.19 to 9.64 (P < .001) but not with G. Sempervirens. In the OF test, G. sempervirens 5 CH significantly increased the time spent and the distance traveled in the central zone (P = .009 and P = .003, resp.), while diazepam had no effect on these OF test parameters. In a subsequent series of experiments, G. sempervirens 7 and 30 CH also significantly improved the behavioral responses of mice in the OF test (P < .01 for all tested variables). Neither dilutions of G. sempervirens affected the total distance traveled, indicating that the behavioral effect was not due to unspecific changes in locomotor activity. In conclusion, homeopathic doses of G. sempervirens influence the emotional responses of mice to novel environments, suggesting an improvement in exploratory behavior and a diminution of thigmotaxis or neophobia.