Response surface methodology (RSM) was applied to optimize the effects of extraction parameters including time, power, temperature and liquid-to-solid ratio on peony seed oil yield. Box-Behnken design (BBD) was employed for optimization of extraction parameters in oil yield that extracted assisting by ultrasonic while petroleum ether as solvent. The chemical composition of peony seed oil under optimal condition in ultrasonic-assisted extract method was analyzed by gas chromatography-mass spectrometry (GC-MS). The optimal conditions were that extraction time 45 min, extraction temperature 45°C, extraction power 90 W and liquid-to-solid ratio 7:1, respectively. Under this condition, the extraction yield value was 33.90% which was with 95% confidence level, hence indicated the reliability of RSM in optimizing ultrasonic-assisted extraction of oil from Paeonia suffruticosa Andr. seed. Three unsaturated fatty acid of peony oil such as n-3 α-linolenic acid (39.75%), n-6 linoleic acid (26.32%) and the oleic acid (23.66%), totally more than 89.00% was determined at optimum condition.