Abstract: To investigate the fire behavior of concrete slabs with in-plane restraints, one fire test was conducted on the full-scale two-way concrete slabs. The testing results included the temperature along the depth, the reinforcement temperature, the vertical and in-plane deflection and constraint reaction forces at the four corners. According to EC2 and ASCE models, the load carrying capacity of four testing slabs with different in-plane restraints was analyzed using five theories. The results showed that the crack parallel to the in-plane restraint force direction was observed on the top surface of the slab. Compared to the out-of-plane deflection, the in-plane deflection perpendicular to the constraint direction was relatively larger and could not be neglected. The in-plane restraint force and failure criterion have an important effect on the limit carrying capacity of the concrete two-way slabs in fire.