Lysimachia liujiangensis, a new species of Lysimachia subg. Idiophyton Hand.-Mazz. from central Guangxi, China, is described and illustrated based on morphological and molecular data. The phylogenetic analyses showed that Lysimachia liujiangensis belongs to subg. Idiophyton and closely related to L. millietii (H.Lev.) Hand.-Mazz.. However, Lysimachia liujiangensis can be distinguished from L. millietii by its stems densely dark purple-glandular at the top and terete in upper part, leaf blade oblanceolate, pedicel 1.3-2.2 cm long, dark purple-glandular, calyx lobes 5-7 mm long, dark purple-glandular on both sides and margin.