Ten-year-old Chan Hang-biu, who used to devour seven pork chops in one sitting, said he considered himself more 'handsome' after losing 4kg in six months.
The boy, who could barely see his toes when standing up, is among the 100 children who joined the Chinese University's weight control programme.
The programme included tailor-made exercising five times a week, a diet control programme, a four-day nutrition camp and also seminars for parents.
Hang-biu, whose weight fell from 42kg to 38kg, said: 'I did not do any exercise in the past. Now I swim and cycle at least twice a week. It is too bad, being fat.
'I learned a lot from the programme and it is fun. Now I eat more vegetables and maybe only one pork chop in a meal.' His classmate, Chan Hoi-ming, said he hated being called 'fatty'.
'I don't want to be a fatty. It's terrible. I want to be slim,' the nine-year-old boy said.
Hoi-ming, who used to eat eight chicken wings in one meal, said he planned to lose at least 5kg in a year.
His weight increased from 48kg to 50kg after the training because of natural growth. But instructors said his body fat was much reduced.
His mother said: 'My son always has to do homework until 10 o'clock at night. How can he have any time to exercise? 'Now he promises to play badminton every Sunday,' Mrs Chan said.
Programme instructors said they would check on the 100 participants in another six months to see if they had maintained their healthy lifestyle and regular exercise.