A method for instant on multimedia playing is provided, which enables a computer to selectively enter an operation mode of an IOMP (Instant On Multimedia Player) program when it enters a power conservation mode. First, a computer system stays in the power conservation mode, until an IOMP activating signal has been received. Next, the computer system saves the hardware information of the computer into a memory. And then a processor of the computer reads an IOMP program from another memory and executes the IOMP program to produce and display a human-computer interface menu, which is provided for users to select files for playing. Next, the processor executes the IOMP program to play the files selected previously. Finally, upon the receipt of a recovery instruction, the computer system saves the hardware information back into the computer to recover the computer to the power conservation mode.