Oryza longistaminata with strong resistance to biotic and abiotic stress was regarded as an excellent gene pool for Asian cultivated rice improvement. Thus, mining and utilization of favorable genes/alleles from O. longistaminata would be important in breeding for Oryza sativa by broadening its genetic basis. To explore blast resistance genes from O. longistaminata, RD23, an indica cultivar from Thailand, was crossed with an accession of O. longistaminata and a set of BC3F7 introgression lines (ILs) was raised. The ILs were screened for blast resistance in natural blast nursery, and three ILs exhibiting high level of resistance to blast disease were obtained. Using a BC4F2 population of IL-E1454/RD23, a novel dominant blast resistant gene, designated as Pi57(t), was mapped on rice chromosome 12 flanked by SSR markers RM27892 and RM28093 within 1.0 cM. Pi57(t) conferred a broad-spectrum resistance to Magnaporthe oryzae isolates collected from Yunnan, P. R. China, and the resistant spectrum was distinguished from five known blast R genes located on chromosome 12. Our results suggest that Pi57(t) would be a promising gene for rice improvement in Yunnan, P. R. China.