This study aims to investigate the taxane diterpenoid constituents of Taxus chinensis var. mairei from Yunnan Province and their myeloma cytotoxic activities.Compounds were isolated and purified from the extract of the leaves and branches of Taxus chinensis var. mairei by using normal-phase,reversed-phase and size exclusion chromatography,and their structures were identified by NMR spectroscopic methods.The isolated compounds were screened for activity against NEK2 over expression myeloma cell proliferation using a CCK-8 assay.Sixteen taxane diterpenoids were obtained and identified as 13-cinnamoyloxy-1-dehydroxy baccatin IV (1),taxusin (2),5α-cinnamoyloxy-9α,10β,13α-triacetoxytaxa-4 (20),11-diene (3),7-deacetoxy taxinine J (4),hongdoushan A (5),11-diene-2α,5α,9α,10β,13β-pentol-2α,9α,10β,13α-tetraacetate-5α-cinnamate (6),taxezopidine H (7),taxinine B (8),taxuyunnanine C (9),1-deoxybaccatin VI (10),19-hydroxybaccatin III (11),baccatin III (12),7,9,13-trideacetyl baccatin VI (13),10-deacetylbaccatin III (14),taxol (15),7-epi-taxol (16).Compound 1 was a new taxane diterpenoid,while compounds 5 and 13 were isolated from Taxus chinensis var. mairei for the first time.The results indicated that compounds 2,6,7 and 11 had notable inhibitory activity on NEK2 over expression myeloma cell proliferation (IC₅₀=24.0,23.5,26.1,18.3μmol/L),and compound 16 (IC₅₀=0.6 μmol/L) had a significant effect.