Based on morphological and molecular data, three new species of the Old World Didymocarpoid Gesneriaceae, Petrocodon laxicymosus, P. longgangensis, and P. pseudocoriaceifolius, are described and illustrated from Guangxi, China. The three new species are most similar to P. coriaceifolius, differing by their texture, size, and shape of leaves, size and pubescence of inflorescence and corolla, anther shape, and pistil length. Additionally, Primulina guangxiensis, one of two species included in Primulina before its recent recircumscription, was unexpectedly found to be nested within Petrocodon in our ongoing phylogenetic analyses, prompting us to make the new combination Petrocodon guangxiensis. The four species of Petrocodon treated here are all rare, known only from a single or a few localities of limestone karsts in Guangxi.