Two new species of genus Diplopeltoides Gerlach, 1962 and two new species of genus Minolaimus Vitiello, 1970 were described based on recently collected specimens from marine sediments of the South China Sea and the East China Sea, respectively. Diplopeltoides conoicaudatus sp. nov. is characterized by annulated cuticle; tiny terminal buccal cavity; short cephalic setae about 2-µm long; loop-shaped amphideal fovea without sclerotized plate; slender and arcuate spicules; triangular gubernaculum possessing a small dorso-caudal apophysis; female with two opposed and reflexed ovaries. Diplopeltoides longifoveatus sp. nov. is characterized by its papilliform cephalic sensilla; long and narrow amphideal fovea with fine transverse striations; inverse S-shaped spicules with a dorsally bent manubrium; gubernaculum with dorso-caudal apophysis; cylindrical tail with round terminal end. Minolaimus multisupplementatus sp. nov. is characterized by cuticle with lateral differentiation of three longitudinal rows of large dots, spiral amphideal fovea with seven turns, pharynx cylindrical without posterior bulb, spicules arcuated with central lamella, gubernaculum arcuate and parallel to spicule, without dorso-caudal apophysis, a papilliform and 29 cup-shaped precloacal supplement; tail conical with long flagelliform portion. Minolaimus apicalis sp. nov. is characterized by cuticle with lateral differentiation of three longitudinal rows of larger dots from the middle of pharynx to the conical portion of tail and a longitudinal row of pores in the pharyngeal region and precloacal region; spiral amphidial fovea with four turns and close to anterior end; pharynx cylindrical with oval posterior bulb, spicules arcuated and proximal end bent dorsally, gubernaculum with a broad curved dorsal apophysis; two sucked-like and six cup-shaped cuticularized precloacal supplements; tail conico-cylindrical with slightly enlarged tip. Updated keys to species of Diplopeltoides and Minolaimus were provided.