This paper documents the richness of parasites inhabiting Rattus tanezumi and Rattus norvegicus. Rattus spp. revealed six ectoparasites, namely: mites genus Chirodiscoides, and Radfordia ensifera, Laelaps nutalli and Ornithonyssus bacoti, fleas Xenopsylla cheopis, and lice Polyplax spinulosa. While infestation with L. nutalli was heavy in 15 (100%) and 13 (86.7%) R. norvegicus and R. tanezumi, respectively, only R. tanezumi harbored Chirodiscoides and P. spinulosa at 80.0%. Endoparasites identified were two kinds of nematodes belonging to genus Nippostrongylus (Class Secernencea) and Capillaria hepatica (Class Adenophorea), and tapeworms identified as genus Raillietina, and Hymenolepis, and Taenia taeniaformis. While all 30 rats showed 100% parasitism with ecto- and endoparasites, Babesia infection was detected only in eight rats (26.6%), with seven cases recorded in male rats. Most dominant endoparasites were Nippostrongylus in R. norvegicus at 73.3%, and R. tanezumi at 100.0%; while R. norvegicus and R. tanezumi revealed 86.6% and 66.6% prevalence with C. hepatica, respectively. Interestingly, Taenia taeniaformis and Raillietina were detected only in R. norvegicus at 80.0% and 20.0% infection, respectively. While both species of rats examined revealed susceptibility to different kinds of parasites, the heavier R. norvegicus seemed to nurture and support greater parasite species richness and density. In view of the argument of a clear accumulation of helminth diversity and species burden with increasing age of rat species and in the absence of information of the ages of rats used in the present survey, studies to cover an expanded rat population in the Philippines is recommended
