In this study, heat transfer and turbulent flow through a twisted-shaped duct with square cross-section has been numerically investigated. The working fluid is taken water (Pr = 2.45). The Reynolds number is chosen between 10000-120000. The edge size of square cross-section, the twist angle and the length of the channel are taken 0.01m, 360 degrees and 0.2 m, respectively. The Navier-Stokes and energy equations have been solved using Simple algorithm and Standart k-epsilon formulation for turbulent flow regime. The governing equations are solved using the commercial code Fluent. The results of the Nusselt number, friction factor and thermal performance factor are presented. It was seen that calculated performance evaluation factor is more than unity in the studied Re numbers for the twisted square duct. It is found that the twisted square duct provides a considerable increase in Nusselt number to 138% over the smooth square duct and a maximum gain of 1.3 on thermal performance factor is obtained for the case of Re=10000.This indicates that the secondary flow occured via the twisted square duct can improve the heat transfer rate.