An apparatus and method for reducing noise of an image sensor are provided. The apparatus includes a noise level setting module setting a noise level representing an image frame expressed as a component in a color space; a kernel generation module generating a kernel for filtering pixels that constitute the image frame based on the set noise level; and a filter application module convoluting the pixels using the generated kernel and normalizing the pixels using the convolution result. Since noise generated by the image sensor can be adaptively reduced, the quality of an output image can be improved.