A fast intramode SKIP detection algorithm based on the rate-distortion (RD) cost for an interframe (P slices) is proposed for H.264/AVC video encoding. There are three types of intrapredictions according to profiles. These are 16×16 and 4×4 intrapredictions for luminance and an 8×8 intraprediction for chroma. For the high profile, an 8×8 intraprediction is added for luminance. The 4×4 prediction mode has nine prediction directions with four directions for 16×16 and 8×8 luma, and 8×8 chrominance. In addition to the intermode search procedure, an intramode search causes a significant increase in the complexity and computational load for an interframe. To reduce the computational load of the intramode search at the interframe, the rate-distortion (RD) costs of the neighborhood MBs for the current MB are used, and we propose an adaptive thresholding scheme for the intraSKIP extraction.