Six species of Monhysteroida are described from the Strait of Magellan and the Beagle Channel, Chile. Three species of which, Sabatieria heipi n. sp., Paramonhystera geraerti n. sp. and Siphonolaimus smetti n. sp., are new to science. Sabatieria heipi n. sp. is characterised by a body length of 1529-1934 µm, cuticle punctuations with lateral differentiation; cephalic setae 5 µm long, amphids spiral with 4.0-4.2 turns, 10-11 µm in diameter; spicules 76 µm (2.1 anal body diameter), with a 6 µm projection in the ventral distal extremity, 11 minute precloacal supplements; tail 3.7-4.7 anal body diameter (abd) long with enlarged tip. Paramonhystera geraerti n. sp. is characterised by a body size of 705-767 µm; head diameter 12 µm, the cephalic setae 6 µm; amphids circular, 9-10 µm in diameter; spicules slender 108-116 µm (5.6 abd) long, 5 precloacal supplements; and tail 4.0-5.2 abd. Siphonolaimus smetti n. sp. is characterised by the long spear (40-45 µm), head diameter 11-12 µm, amphids circular, 12-13 µm in diameter or 50-57% of corresponding body diameter; the spicules 55 µm and 1.5 abd; tail conical, 2.8 abd (males) and 4.0 abd (females) long. Three other species, i.e. Metacomesoma cyatholaimoides Wieser, 1954, Paramonhystera biforma Wieser, 1956 and P. megacephala (Steiner, 1916) are redescribed. A key of all known species of Paramonhystera is proposed.