This paper analyzes the effect of random phase shifts in the underlying clock signals on the operation of several basic Quantum-dot Cellular Automata (QCA) building blocks. Such phase shifts can result from manufacturing variations or from uneven path lengths in the clocking network. While previous literature has proposed various clock distribution architectures and also provided analysis of manufacturing variations on QCA layouts, so far no literature is available on the characterization of effects resulting from the lack of phase synchronization in the QCA clocks. We perform numerical simulations of these basic building blocks using two different simulation engines available in the QCADesigner tool. We assume that the phase shifts are characterized by a Gaussian distribution with a mean value of i 2 , where i is the clock number. Our results indicate that the sensitivity of building blocks to phase shifts depends primarily on the layout of the building block, and that most building blocks were able to operate properly under random phase shifts characterized by = 5% of /2.