The deceased were identified as Abu Taher, 60, his wife Ayesha Begum, 50 and their grandson 18-month old Rashed, son of Rubel Ahmed.
According to fire service control room, the fire broke out at Azam Nagar slum around 7:30pm.
On information eight vehicles of two fire stations rushed to the spot and brought the blaze under control after two hours of frantic efforts.
Later, they retrieved the three charred body from the slum, said deputy additional director Farid Ahmed Chowdhury of Chattagram divisional fire service media cell.
According to slum dwellers, at least 100 shanties were gutted in the fire.
Besides, at least 28 people were injured in the incident.