The paper focuses on the effect of openings on punching shear strength of post-tensioned flat slabs supported on square columns. Five slab specimens had been tested under concentrated load and it was found, that the openings reduce punching strength considerably. The accuracy of the strut-and-tie model together with the design equations of ACI, CSA, ECP, BS and CEBcodes of practice has been. For the prediction of the punching shear strength of the tested specimens and for evaluating the effect of the near column openings, the strut-and-tie model proposed by Emad Raouf, 2010 for calculating the punching shear strength of non-pre- stressed slabs are used. In addition, proposed methods for calculating the punching shear strength of post- tensioned slabs using modified ECP equation are introduced and evaluated using the present experimental results in addition to 40 experimental results from the literature. The proposed strut-and-tie model is found to be accurate.