Three year-old peony (Paeonia. lactiflora Pall. cv. Taebaek) was cultivated in green-house at Jan. 15, Feb. 15, or Mar. 15, respectively. The mean of temperature during the forcing cultivation was higher (air; $1.0{sim}11.1^{circ}C$, soil; $1.1{sim}7.4^{circ}C$) than that of open-field condition. From sprouting to flowering in peony cultivated at Jan. 15 was about 54 days, which is shorted the cut flower periods (ca. 26 days) compared with the open-field cultivation. However, earlier forcing cultivars were very susceptible to pathogens such as powdery mildew or gray mold. The yield in green house was also lower than in the open-field cultivation. The content of bioactive compounds such as paeoniflorin and albiflorin in green-house cultivars was similar that of open-field cultivars. These results showed the forcing cultivation time of peony at Feb. 15 in green-house was most desirable for commercialization.