This paper proposes a very small on-chip multimedia real-time OS for embedded system LSIs, and demonstrates its usefulness on MPEG-2 multimedia applications. The real-time OS, which has a new cyclic task with suspend and resume for interacting hardware (HW) / software (SW) of embedded system LSIs, implements the minimum set of task, interrupt, and semaphore managements on the basis of an analysis of embedded software requirements. It requires only about 2.5 K bytes memory on run-time, reduces redundant conventional cyclic task execution steps to about 1/2 for HW/SW interactions, and provides sufficient performance in real-time through implementing two typical embedded software for practical multimedia system LSIs: an MPEG-2 system protocol LSI and an MPEG-2 video encoder LSI. This on-chip multimedia real-time OS can be easily integrated on many embedded system LSIs and provides efficient embedded software design environment.