Plasmodium knowlesi is a significant cause of simian (zoonotic) malaria in Sarawak, Malaysia. Until 2018, only one study had been carried out in Sarawak to identify of P. knowlesi, where Anopheles latens was incriminated as the vector in Kapit Sarawak. A comprehensive entomological investigation was conducted in Limbang, Sarawak, following an imported Plasmodium falciparum malaria case in March 2018. The objective was to identify the vector species and determine the presence of malaria parasites in mosquitoes. Human Landing Catch (HLC) and Human Bait Trap (HBT) sampling were conducted from April 18 to 21, 2018, between 1800 and 2400 hours. Female Anopheles mosquitoes were captured, identified by means of microscopy, and dissected to examine oocysts and sporozoites. Positive slides and the remaining undissected Anopheles were sent to the Malaysian Institute of Medical Research (IMR) for species confirmation by means of polymerase chain reaction (PCR) and molecular testing for malaria parasites. A total of 117 female Anopheles mosquitoes were examined. Of these, 29 were identified as Anopheles donaldi based on their morphology, while the rest comprised An. leucosphyrus, An. barbirostris and An. kochi. One An. donaldi that was dissected was found to have oocysts on its midgut and confirmed as P. knowlesi through molecular analysis. Molecular testing of 36 specimens also revealed 4 abdominal and 2 thoracic samples that were positive for P. knowlesi, including the sample slide, and 6 abdominal and 1 thoracic sample that were positive for P. vivax. This study marks the first report of P. knowlesi in An. donaldi (Barbirostris group) in Sarawak, Malaysia, a species that was not previously associated with Plasmodium knowlesi. These findings suggest that Anopheles species outside of the An. leucosphyrus group may also serve as vectors for P. knowlesi. The detection of both P. knowlesi and P. vivax in mosquitoes indicates the vulnerability of this locality to malaria transmission, emphasizing the need for sustained malaria control efforts.