The 17β-estradiol (E2) plays an important role on the control of energy homeostasis and its effects are similar to leptin’s effects. Leptin plays its actions on energy balance through the activation of PI3K pathway and requires STAT3 activation. It has been suggested that E2 could act through common mechanisms of leptin action to regulate body weight. In this study, to assess the effects of E2 on energy balance and its interaction with leptin, we used ovariectomized Wistar rats (240-280g) treated with E2 (OVX + E) or oil (OVX) for 8 consecutive days. On the 8th day rats were icv injected with leptin (3.5 µg/2µl) or vehicle (saline). Food intake and body weight were daily evaluated. We also determined the expression of UCP-1 protein in the brown adipose tissue (BAT), expression of phosphorylated STAT3 (p-STAT3) in the mediobasal hypothalamus by Western blotting and expression of p-STAT3 by immunohistochemistry in the arcuate nucleus (ARC), ventromedial (VMH), paraventricular (PVN) and retrochiasmatic (RCA) nuclei. We also evaluated the effects of E2 on food intake, body weight and protein expression of UCP-1 in OVX and OVX + E rats treated with PI3K inhibitor (LY294002, 1nmol/2ul, icv) or vehicle, followed by icv injection of leptin. Values are means ± SEM, compared by Wilcoxon-Mann-Whitney test or two or three way ANOVA. Compared to OVX group, OVX-E group showed lower daily food intake (9.3±0.16 g/100g vs 8.4±0.15 g/100g; p<0.05), body weight gain (51±2.4 g vs 29.7±2.3 g; p<0.001), and retroperitoneal adipose tissue content (0.6±0.08 g/100g vs 0.38±0.05 g/100g; p<0.05). Leptin induced a lower (p<0.05) food intake (OVX: vehicle, 3.3±0,1g/100g vs leptin, 2.4±0.18 g/100g; OVX+E: vehicle, 2.8±0.18 g/100g vs leptin, 2.1±0.16 g/100g) and body weight gain (OVX: vehicle, 5±0.97g vs leptin, -0.69 ± 1.7g; OVX+E: vehicle, 2.8 ±0.9g vs leptin, -4,6±1.1g) in both groups OVX and OVX + E. E2 potentiated the effect of leptin on body weight, but it did not affect the hypophagic effect of leptin. Leptin increased the expression of UCP-1 in the BAT and this response was even higher in the OVX + E group. Leptin increased p-STAT3 expression in the HMB of OVX and OVX + E groups. In the OVX+E group there was an increase of p-STAT-3 expression after leptin stimulation in the nuclei ARC and VMH, compared to OVX group. PI3K inhibitor reversed the hypophagic effects of leptin in the OVX group and OVX + E, and it partially reversed the body weight loss induced by leptin in OVX + E group. PI3K inhibitor also reversed the increase of UCP-1 expression in the BAT induced by leptin in the OVX + E group. These data suggest that the involvement of estradiol in the energy homeostasis is associated with an increase of leptin action to activate STAT3 in the hypothalamus. Moreover, the interaction of estradiol and leptin signaling is mediated at least in part by the PI3K pathway.