The genus Macromitrium is one of the richest genera of mosses in New Caledonia, although unrevised to date, with 44 names currently accepted. A new species, Macromitrium humboldtense, is described and illustrated here. It is characterized by 1) a soft and shaggy habit, when dry with the leaves irregularly individually twisted and loosely spirally arranged, with their thin points unevenly oriented; 2) branches relatively short and crowded; 3) branch leaves large (> 3.6 mm), narrowly lanceolate, regularly tapering from basal 1/8 of the leaf, long acuminate, ending in a piliform apex; 4) upper cells papillose, basal cells mainly smooth; 5) setae long (> 15 mm), calyptrae glabrous. Comparison with piliferous species of Macromitrium in neighbouring countries is given. Ecological and geographical features for the three long cuspidate Macromitrium in New Caledonia are discussed.