A new free-living marine nematode species Hopperia sinensis sp. nov. from mangrove forests of Fujian Province, China, is identified and illustrated. Hopperia sinensis sp. nov. is characterized by its cephalic setae 2.4–2.8 μm long or 17%–20% head diameter, and amphids of 2.25–2.5 turns. Lateral differentiation appears with larger, more irregularly distributed dots behind 3–5 transverse rows of dots posterior to amphid. Buccal cavity is consisted of a shallow and weakly sclerotized cup-shaped portion with strongly sclerotized walls of 18–21 μm deep. There are three sclerotized and size-equally pointed teeth at the junction between the two parts. Spicules of 41–45 μm long are slightly curved with broadband velum and central strips at the proximal end. The gubernacula, with apparent lateral guiding pieces, are formed by one central tubular piece that is weakly sclerotized with 11–16 μm long dorso-caudally directed apophyses. There are 13–14 fine tubular precloacal supplements. Conico-cylindrical tail gradually tapers till pointed tail tip. Female is similar to male, but have a longer body and tail. Ovaries are opposed and outstretched, with anterior ovary to the left and posterior ovary to the right of the intestine. A pictorial key to all the valid known species in genus Hopperia is given. Nov. Is mangrove forests of Fujian Province, China, identified and illustrated. Hopperia sinensis sp. Nov. Is characterized by its cephalic setae 2.4-2.8 μm long or 17% -20 Lateral differentiation appears with larger, more irregularly distributed dots behind 3-5 transverse rows of dots posterior to amphid. Buccal cavity is consisted of a shallow and weakly sclerotized cup-shaped portions with strongly Sclerotized walls of 18-21 μm deep. There are three sclerotized and size-equally pointed teeth at the junction between the two parts. Spicules of 41-45 μm long are slightly curved with broadband velum and central strips at the proximal end. The gubernacula , with apparent lateral guiding pieces, are formed by one central tubular piece that is weakly sclerotized with 11-16 μm long dorso-caudally directed apophyses. There are 13-14 fine tubular precloacal supp lements. Conico-cylindrical tail gradually tapers to pointed tips tip. Female is similar to male, but have a longer body and tail. Ovaries are opposed and outstretched, with anterior ovary to the left and posterior ovary to the right of the intestine. A pictorial key to all the valid known species in genus Hopperia is given.