In the data transmission method of an HSDPA system according to the present invention, a transmitter transmits Data Blocks each composed of one or more data units originated from a same logical channel, and a receiver receives the Data Block through a HS-DSCH and distributes the Data Block to a predetermined reordering buffer. Since each Data Block is composed of the MAC-d PDUs originated from the same logical channel, it is possible to monitor the in-sequence delivery of the data units, resulting in reduction of undesirable queuing delay caused by logical channel multiplexing.