Weight re-gain within 2 y after Roux-en-Y gastric bypass (RYGB) is significantly associated with increased intake of and cravings for sweet foods. Here we describe a novel model of this late increase in sweet appetite. Ovariectomized RYGB and Sham-operated rats, with or without estradiol treatment, were maintained on Ensure liquid diet and offered a low-energy, artificially sweetened diet (ASD) 2 h/d. First, we tested rats more than six months after RYGB. ASD meals were larger in RYGB than Sham rats, whereas Ensure meals were smaller. General physical activity increased during ASD meals in RYGB rats, but not during Ensure meals. Second, new rats were adapted to ASD before surgery, and were then offered ASD again during 4–10 wk following surgery. Estradiol-treated RYGB rats lost the most weight and progressively increased ASD intake to >20 g/2 h in wk 9–10 vs. ∼3 g/2 h in Sham rats. Finally, the same rats were then treated with leptin or saline for 8 d. Leptin did not affect body weight, Ensure intake, or activity during meals, but slightly reduced ASD intake in estradiol-treated RYGB rats. Food-anticipatory activity was increased in estradiol-treated RYGB rats during the saline-injection tests. Because increased meal-related physical activity together with larger meals is evidence of hunger in rats, these data suggest that (1) RYGB can increase hunger for a low-energy sweet food in rats and (2) low leptin levels contribute to this hunger, but are not its only cause. This provides a unique rat model for the increased avidity for sweets that is significantly associated with weight recidivism late after RYGB.