An image sensor and an image processing system including the same are provided. The image sensor includes a pixel array including a plurality of pixels each connected to one of first through m-th column lines to output a pixel signal, where “m” is an integer of at least 2; analog-to-digital converters each configured to receive the pixel signal corresponding to one of the first through m-th column lines, to compare the pixel signal with a ramp signal, and to convert the pixel signal to a digital pixel signal; and a blocking circuit connected to an input terminal of at least one of the analog-to-digital converters to block an influence of an operation of others among the analog-to-digital converters.