A device for removing mosquito noise and associated method is provided to adaptively determine a proper strength for removing the mosquito noise according to image complexities, thereby removing the noise while maintaining the quality of image details. The device includes a buffer, a lookup table, and a strength determining unit. The buffer stores a pixel matrix having a target pixel. The lookup table stores a plurality of coefficients. The strength determining unit, coupled to the buffer and the lookup table, detects the image complexities of the pixel matrix and looks up the lookup table according to the image complexities of the pixel matrix, so as to output a strength coefficient for removing the mosquito noise.