A method for transferring variable isochronous data and an apparatus therefor are provided. The method for transferring variable isochronous data includes the steps of (a) determining isochronous transfer to be terminated when the bus is in an idle state for a time interval which is larger than an isochronous gap period, (b) detecting a residual gap having a time interval which is larger than the time interval of an isochronous gap and smaller than the time interval of a subaction gap, (c) checking whether bandwidth for the transfer of isochronous data remains when the residual gap is detected in the step (b), and (d) transferring the isochronous data when it is determined that the bandwidth for the transfer remains in the step (c). According to the variable isochronous data transfer method, it is possible to maximize the isochronous transfer by selectively using the residual bandwidth, which is assigned for the transfer of the isochronous data but is not used for the real transfer of the isochronous data, for the transfer of the isochronous data.