An input data alignment circuit includes a data sampler, a frequency divider, a polarity determination block, and a data alignment block. The data sampler provides a data sequence based on data serially input according to a data strobe signal. The frequency divider generates a data alignment signal based on a divided frequency of the data strobe signal. The polarity determination block determines a polarity of the data alignment signal and provides a control signal based on the determined polarity. The data alignment block aligns the data sequence in parallel according to data alignment signal and control signal and generates output data.