Abstract: Downy mildew caused by Peronosclerospora philippinensis (Weston) Shaw is one of the most persistent diseases encountered by maize producers in the Philippines. Improved durable resistant host plant could provide an effective way of both increasing and stabilizing corn production in affected areas. An extensive research to study the genetics of downy mildew resistance in maize against the UPLB isolate pathogen using generation mean analysis and to locate QTL conferring resistance against P. philippinensis causing Philippine downy mildew were done. The genetics of resistance to P. philippinensis was studied in progenies derived from crosses between the resistant inbred P 345 and Nei 9008 and susceptible inbred Pi 17 and Pi 23. Plant generations used in this study were the PS (susceptible lines); PR (resistant lines); F1, F2, F3, BS and BR. Analysis of generation means indicates that additive-dominance gene effect plays an important role in all components of resistance in all crosses involving Nei 9008. On the other hand, additive-dominance with epistatic gene effect plays an important role for all components of resistance involving P 345. QTL conferring resistance against P. philippinensis was observed in a BC1F2 population developed from a cross between Pi 23 and P 345. QTL analysis of the different components of resistance showed that a total of twenty-seven regions distributed in nine chromosomes of the maize genome were associated in varying degrees with resistance to P. philippinensis. Four regions located in chromosomes 1, 5, 6 and 8 were associated with disease incidence and disease severity. Results suggest that it may be possible to incorporate QTLs of various components of resistance into the elite inbred line Pi 23 using marker aided selection.