In this paper, five new species of Begonia from western Sarawak are described and illustrated: B. cruentospirituna C.W. Lin, B. galaxia C.W. Lin, B. opaca C.W. Lin & C.-I Peng, B. suyenii C.W. Lin and B. zygia C.W. Lin & C.-I Peng. All species belong to section Petermannia. The materials studied were mainly from plants cultivated in nurseries and measurements made in the description were mostly taken based on images of living plants in the field. In addition to the taxonomic accounts, color plates, line drawings, and comparisons with phenetically similar species are provided to aid in identification.