A method of decoding a video by using data unit merging, the method comprising: obtaining, from a received bitstream, a skip flag for a coding unit which indicates whether a encoding mode for the coding unit is a skip mode; and when the skip flag indicates a non-skip mode, obtaining, from the received bitstream, information about a partition type for prediction and determining at least one partition from the coding unit using the information about a partition type; obtaining a merge flag for the partition, from the received bitstream; when the merge flag for the partition indicates a merge mode, obtaining a merge index for the partition and determining motion information for the partition using motion information of a block which the merge index indicates, performing motion compensation on the partition using the determined motion information of the block which the merge index indicates; and when the merge flag for the partition indicates a non-merge mode, obtaining motion information for the partition from the received bitstream, performing motion compensation on the partition using the obtained motion information; characterized in that the merge index indicates one block among a merge candidate block group comprising one or more blocks from among the following three_neighboring blocks of the partition: a left-lower block located on a left side of a leftmost block among lower blocks directly below a lower border of the partition, a left-upper block located on a left side of a leftmost block among upper blocks directly above an upper border of the partition, the left-upper block being located above an uppermost block among the left blocks adjacent to the left border of the partition, and a right-upper block located on a right side of a rightmost block among the upper blocks directly above the upper border of the partition. obtaining, from a received bitstream, a skip flag for a coding unit which indicates whether a encoding mode for the coding unit is a skip mode; and when the skip flag indicates a non-skip mode, obtaining, from the received bitstream, information about a partition type for prediction and determining at least one partition from the coding unit using the information about a partition type; obtaining a merge flag for the partition, from the received bitstream; when the merge flag for the partition indicates a merge mode, obtaining a merge index for the partition and determining motion information for the partition using motion information of a block which the merge index indicates, performing motion compensation on the partition using the determined motion information of the block which the merge index indicates; and when the merge flag for the partition indicates a non-merge mode, obtaining motion information for the partition from the received bitstream, performing motion compensation on the partition using the obtained motion information; characterized in that the merge index indicates one block among a merge candidate block group comprising one or more blocks from among the following three_neighboring blocks of the partition: a left-lower block located on a left side of a leftmost block among lower blocks directly below a lower border of the partition, a left-upper block located on a left side of a leftmost block among upper blocks directly above an upper border of the partition, the left-upper block being located above an uppermost block among the left blocks adjacent to the left border of the partition, and a right-upper block located on a right side of a rightmost block among the upper blocks directly above the upper border of the partition. a left-lower block located on a left side of a leftmost block among lower blocks directly below a lower border of the partition, a left-upper block located on a left side of a leftmost block among upper blocks directly above an upper border of the partition, the left-upper block being located above an uppermost block among the left blocks adjacent to the left border of the partition, and a right-upper block located on a right side of a rightmost block among the upper blocks directly above the upper border of the partition.