Abstract: To analyze the fire behavior of two-way simply-supported slabs with in-plane restraints, two fire tests were conducted on full-scale concrete slabs subjected to in-plane loads and lateral loads. The testing results include the temperature fields along the depth of the slabs, reinforcement temperature, out-of-plane and in-plane deflection and constraint reaction at the corners. The present results are compared with the relevant tests. In addition, based on the EC2 and ASCE constitutive models, a program was developed to analyze the temperature, deflection and the mechanical mechanism of tested concrete slabs. The results indicate that the cracking patterns and deflection of the concrete slabs with in-plane restraints were different from those of simply supported slabs, and the integrity failure easily occurred. The corner crack distribution has an important effect on the constraint forces. Furthermore, the constitutive models have a vital influence on the mechanical mechanism of the restrained slabs in fire.