Morphologically novel species of the ant-mimetic plant bug genus Pilophorus Hahn from Thailand are reviewed, with photographic images of live individuals. Three species, Pilophorus barbiger, P. giraffoides, and P. portentosus, are described as new, in addition to two known Thai species, P. maculatus (Schuh) and P. pleiku (Schuh), which are also diagnosed. The female of P. pleiku is reported for the first time. The biology and immature forms are documented for P. pleiku and P. barbiger, which were observed to be associated with ants on the rubiaceous broadleaf, Gardenia sootepensis Hutch. The systematic position of such morphologically novel species is discussed. Pilophorus palawanus (Schuh) is newly recorded from Singapore.