Manglietia guangnanica D. X. Li & R. Z. Zhou (Magnoliaceae), a new species from Yunnan, China, is described and illustrated. Its pollen morphology, ecology, and conservation status are presented. Manglietia guangnanica is closely related to M. pachyphylla Hung T. Chang, M. crassipes Y. W. Law & M. fordiana Oliv. The new species is distinguished from M. pachyphylla by its narrower leaves (4–6 cm vs. 6–10 cm), the glabrous abaxial surfaces (vs. pubescent), the shorter peduncles (1.4–1.8 cm vs. 2.3 cm) and pedicels (0.4–0.6 cm vs. 0.7–1.8 cm), the smaller gynoecia (1.7–1.9 cm vs. 2.1–2.9 cm) and fewer carpels (29 to 34 vs. 54 to 61), and fewer ovules (six to eight vs. [eight]nine to 17[18] ovules per carpel). Manglietia guangnanica differs from M. crassipes by its narrower leaves (4–6 cm vs. 6–9.3 cm), the ovoid gynoecia and flower buds (vs. elliptic), the sparse sericeous indument on the buds, the pale green color of the branchlets and abaxial blade surfaces (vs. these surfaces glaucous), and the fewer carpels (29 to 34 vs. 37 to 40) and ovules (six to eight vs. eight to 13[14] ovules per carpel). The new species also differs from M. fordiana by its branches (glabrous except the young nodes that are sparsely pubescent with erect brown trichomes vs. an indument of appressed, rusty brown trichomes), the peduncles, abaxial surfaces of leaves, and bottoms of outer tepals (glabrous vs. appressed, rusty brown trichomes), the petioles (sparsely brown pubescent and later glabrate vs. appressed, rusty brown trichomes), fewer ovules (six to eight vs. eight to 14 ovules per carpel), as well as the longer stigmas and beaks (stigmas 4–5 mm vs. 1–2 mm, beaks 2–4 mm vs. 1–2 mm).