Objective: Increased QTc dispersion is a predictor for ventricular arrhythmias. The aim of this study was to investigate whether QTc dis- persion decreases after weight loss program with diet and medical treatment. Methods: Total 30 (24 women and 6 men, mean age: 44±8 years) obese subjects who lost at least 10% of their original weight after 12 week weight loss program were included in present study. Obesity was defined as ≥30 kg/m2 of body mass index (BMI). Normal weight was defined as ≤ 25 kg/m2 of BMI. Results: After 12 week weight loss program, BMI decreased from 42±5 kg/m2 to 36±4 kg/m2 (p<0.001) and mean weight of obese subjects decreased from 110±17 kg to 95±15 kg (p<0.001). The mean amount of weight loss was 14.5±5.0 kg (range 9-32 kg). The average percent of weight loss was 13% (10.0%-20.3%). Maximum QTc interval (from 446±19 ms to 433±27 ms, p=0.024) and QTc dispersion (from 66±18 ms to 52±25 ms, p=0.024) significantly decreased after weight loss program. A statistically significant correlation was found between decrease in level of QTc dispersion and amount of weight loss (r=0.487, p=0.007). Conclusion: Substantial weight loss in obese subjects is accompanied by significantly decreased QTc dispersion. The degree of QTc dis- persion reduction is associated with amount of weight loss.