Late blight caused by Phytophthora infestans is a disease devastating tomato grown in Vietnam, especially in a rainy season in highland areas and the winter- spring season in Red river delta where the weather is cool and humid. By artificial inoculations with fresh isolates collected in different locations, all local accessions and currently cultivated tomato varieties showed susceptible to the pathogen. Among introduced accessions carrying genes Ph1, Ph2, and Ph3, only gene Ph3 was identified to be stably resistant to P.infestans isolates collected in different agro-ecological regions of Vietnam. Hybrids with a heterozygote of this gene were moderate resistance, probably inferring that Ph3 was a partially dominant gene. These findings can be applied further in breeding tomato resistant to late blight in Vietnam.