Twenty new polyoxygenated labdane diterpenoids (1-20) were isolated from the aerial parts of Leonurus macranthus. Their structures were elucidated on the basis of spectroscopic and spectrometric data (1D and 2D NMR, IR, and HRESIMS). The absolute configurations of macranthin A (1) and 6-O-deacetylmacranthin A (2) were determined by single-crystal X-ray crystallographic analysis and a modified Mosher's method, respectively. Compounds 1-9, 12, 14, and 19 showed inhibition of nitric oxide production in lipopolysaccharide-activated BV-2 microglial cells with IC50 values of 10.0-63.7 μM.