A method and an apparatus for transmitting and receiving packets in a broadcasting system are provided. The present disclosure allocates a padding size field by using padding octets, and thus can increase transmission efficiency. Also, the present disclosure does not restrict the number of padding octets while maintaining compatibility with existing disclosures, and thus can carry out as much padding as desired and as necessary. In addition, the present disclosure variably allocates the padding size field depending on the number P of padding octets, and thus can increase header efficiency. Furthermore, since the number of padded octets in a header is immediately known, the size of an actual payload is known in advance, and thus rapid transmission is possible.