This study was performed to investigate the effect of of transdermal testosterone gel (TTG) on controlled ovarian stimulation (COS) and IVF outcomes and ovarian morphology according to pretreatment duration in poor responders. A total of 120 women were recruited for this pilot study. They were randomized into control, 2 weeks, 3 weeks or 4 weeks TTG treatment groups. For three TTG treatment groups, 12.5 mg TTG was applied daily for 2 weeks, 3 weeks or 4 weeks in preceding period of study stimulation cycle. After 3 weeks of TTG pretreatment, significant increase of antral follicle count (AFC) and significant decreases of mean follicular diameter (MFD) and resistance index (RI) value of ovarian stromal artery were observed (p=0.026, p<0.001, p<0.01, respectively). The total dose of rhFSH administered for COS significantly decreased after 3 and 4 weeks TTG treatment both compared with control group (p<0.001, p<0.001). The numbers of oocytes retrieved and mature oocytes were significanty higher in 3 and 4 weeks TTG treatment groups than control group (p<0.001, p<0.001 in the number of oocytes retrieved; p<0.001, p<0.001 in the number of mature oocytes). The clinical pregnancy rate and live birth rate were increased only in 4 weeks TTG treatment group compared with control group (p=0.030 and p=0.042, respectively). These data demonstrated that TTG pretreatment for 3 to 4 weeks increases AFC and ovarian stromal blood flow, thereby potentially improving the ovarian response to COS and IVF outcome in poor responders undergoing IVF/ICSI.