Aster spathulifolius Maxim (AS), a perennial herb of the genus Aster within the family Asteraceae, induced weight loss in a rat model of diet-induced obesity. We hypothesized that AS could also reduce body weight in obese humans. Therefore, we performed a randomized, double-blind, placebo-controlled clinical trial in Korea to evaluate the effect of AS extract (ASE) on body weight and fat mass and its safety in obese humans. Forty-four obese participants (body mass index [BMI], 25-30 kg/m(2)) aged ≥20 years were randomly assigned to the placebo or ASE group (700 mg/d of ASE) and were instructed to take a once-daily pill for 12 weeks. Weight, BMI, waist circumference, fat mass (measured using bioimpedance, dual-energy X-ray absorptiometry, and computed tomography), and laboratory tests were assessed at baseline and at 12 weeks. Body weight significantly decreased after 12 weeks of treatment in the ASE group (placebo vs ASE: -0.08 ± 2.11 kg vs -3.30 ± 3.15 kg, P < .05), and so did body fat mass (placebo vs ASE; bioimpedance method: -0.51 ± 1.89 kg vs -2.38 ± 2.30 kg, P < .05; dual-energy X-ray absorptiometry: 0.38 ± 1.59 kg vs -2.26 ± 2.37 kg, P < .05). Changes in lipid profiles, fasting plasma glucose, and hemoglobin A1c did not differ between the 2 groups. No drug-related adverse events were observed during the study. In conclusion, ASE significantly decreases body weight and fat mass in obese humans, suggesting that ASE may be a potential therapeutic candidate for reducing obesity.