Provided are a time-division data multiplexing/demultiplexing system and method capable of preventing errors in processing data signals which occur due to a phase difference between data signals and a multiplexing reference clock in a multiplexing process or a phase difference between a multiplexed data signal and a demultiplexing reference clock in a demultiplexing process. The time-division data multiplexing system includes: a phase adjusting unit which adjusts a phase of each of a plurality of data signals having different phases from one another for enabling the data signals to be time-division multiplexed when a plurality of values of the data signals indicate a stable state; and a multiplexer time-division multiplexing the phase adjusted data signals according to a multiplexing reference clock.