A video encoding method and apparatus, and a video decoding method and apparatus, which are capable of improving efficiency of encoding a luminance component video signal by predicting information on various encoding modes of the luminance component video signal by using a result obtained by encoding a chrominance component video signal, are provided. Accordingly, a block mode and an intra-prediction mode of the luminance component video signal are predicted from a previously encoded and recovered chrominance component video signal, and the predicted block mode and the predicted intra-prediction mode are used to encode the luminance component video signal.