The aim of this study was to evaluate the effect of menstration among the influencing factors for the GnRH agonist (as G: depot goserelin 3.6 mg) therapy prior to the planned myomectomy for women who wanted to preserve their fertility. We reviewed total 48 patients. with the G therapy prior to the planned myomectomy from August 1st, 2005 to August 31st, 2006. The patients were classified by the G group (n=28) and the immediate surgery (as S) group (n=20). The G group (n=19) underwent the G therapy for 3 month courses, and then the efficacy was evaluated by menstruation and the myoma volumes. In the G group (n=19), therapy was effective, and the mean age was $32.4{pm}6.5$ years. After the completion of G therapy, the mean volume of the myoma by ultrasonography was reduced to $85.2{pm}71.2cm^3$ comparing of $430.6{pm}248.8cm^3$ at first visit. The 11 patients had menstruation and the rest 8 patients with amenorrhea had less reduced volume of the myoma ($124.05{pm}79.85cm^3;v.s.;329.41{pm}234.0cm^3$ p<0.05). In the immediate S group, the myoma volumes by sonography was also checked for accuracy (${alpha}=1.0$). As the result, the initial myoma volume had the positive correlations to the effectiveness with G therapy. However, the occurrence and frequency of the menstruation during the G therapy had a negative correlation. In conclusion, the use of G prior to the planned myomectomy was effective in reducing myoma volume and the menstruation.