Recently the geometric complexity and irregularity of building structures have been rapidly increasing, which signifcantly afects the seismic performance of the structures. Al-Ali and Krawinkler (1998) investigated the seismic behavior of building structures with vertical irregularities, and found that the seismic response of building structures is more sensitive to stifness and strength irregularities than to mass irregularities. Soni and Mistry (2006) carried out review of studies on the seismic behavior of vertically irregular structures along with their fndings. Scott et al. (2007) explored the structural challenges that are created by buildings with unique geometries or articulated forms, and discussed some of economic design and construction techniques. Sarkar et al. (2010) proposed a new method of quantifying irregularity in building frames with vertical geometric irregularity accounting for dynamic characteristics, and provided a modifed empirical formula for estimating fundamental period. Vollers (2008) proposed a morphological scheme which enables data to be retrieved on sustainable performance of building shapes. He categorized the geometry of high-rise buildings into Extruders, Rotors, Twisters, Tordos, Transformers, and Free Shapers depending on their form-generation method. Kim and Kong (2013) investigated the progressive collapse-resisting capacities of rotor-type diagrid structural system buildings based on arbitrary column removal scenario, and found that the rotor-type diagrid structures showed sufcient progressive collapse-resisting capacity regardless of the diferences in shapes as long as they were designed to meet the current design code. Kim and Kwon (2014) investigated the progressive collapse and seismic performance of twisted diagrid buildings. Recently Gerasimidis et al. (2016) proposed a simple approach for optimizing diagonals of steel diagrid tall buildings and discussed on robustness of tall building structures. The current seismic design codes, however, do not distinguish seismic response factor depending on vertical geometry of structures. The seismic response factors, especially the response modifcation factor, are important in the evaluation of design seismic load of structures. In the design of tall buildings the response modifcation factor signifcantly afects the overall cost of construction and safety. In this study the seismic performance of the Rotortype or axi-symmetric tall building structures was evaluated by nonlinear static and dynamic analyses. The validity of the seismic performance factor used for seismic design was also investigated following the procedure recommended in the ATC-63 (2009) report. For analysis models, thirty-threestory convex, concave, and gourd-type axi-symmetric buildings were designed to have similar foor areas using diagrid structure system, and their performances are compared with that of a regular moment frame building. Seismic fragility analyses were carried out using twenty-two pairs of earthquake records to compare the probability of failure of model structures for a given earthquake intensity. The efect of variation in the overall shape of axi-symmetric tall buildings on the seismic performance was also evaluated.