An ultra-compact low-loss 1×4 optical power splitter with a splitting ratio of 1∶2∶4∶8 is proposed and demonstrated on a 220-nm-thick silicon-on-insulator (SOI) platform at the C band. The splitter is based on two stages of a cascaded 1×3 multimode interference (MMI) coupler and a 4×4 MMI coupler. The footprint of the device is 124.0  μm×6.4  μm, which is more compact than the traditional scheme of four-stage cascaded 1×2 MMI couplers. Phase shifters based on taper waveguides are incorporated in the device as the connection of two MMI couplers. The fabricated device exhibits a 3 dB power difference with a deviation of less than 0.88 dB from 1530 nm to 1570 nm. The average power difference is 3.14 dB at the center of the C band with an insertion loss of 1.84 dB.