In this paper, four new species of malacocarpic Sargassum are described: S. fuliginosoides Tseng et Lu sp. nov. is characterized by its discoid holdfast, the presence of the bulbs on the basal parts of the primary branches and very thick, lanceolate leaves. S. gemmiphorum Tseng et Lu sp. nov. is characterized by its conical holdfast, usually branched axis and very long, narrow, thin, denticulate leaves. S. shandongense Tseng, Zhang et Lu sp. nov. is characterized by its discoid holdfast, flattened primary branches, its leaves mostly entire or wavy at the margins and its racemose to paniculate receptacles. S. qingdaoense Tseng et Lu sp. nov. is characterized by the presence of the glandular dots on the ultimate branches and elongated lanceolate, acute, mostly wavy leaves.