Heat transfer characteristics of a circular cylinder in the branch of a T-junction duct are experimentally investigated in a low-speed wind tunnel with Reynolds number of Reb = 9163. Local and average heat transfer distributions around the circular cylinder are obtained for the cylinder positions ranging from 0.5 to 13 and the velocity ratios ranging from 0.117 to 0.614. It is found that the overall heat transfer characteristics in a T-junction duct at high velocity ratio are lower than those at low velocity ratio, and both are higher than those in the straight duct. The local Nusselt number in the T-junction duct is an asymmetrical distribution and weakens with increasing velocity ratios and/or positions of the cylinder. The angles of the front and rear stagnation points in the T-junction duct are the same as those in the straight duct at certain velocity ratio and/or position of the cylinder. However, the angles of the front and rear separation points in the T-junction duct do not match those in the straight duct. Both the heat transfer correlation coefficients and the amplitude ratios increase with increasing positions of the circular cylinder and/or velocity ratios.