Imidazolinones, which target the acetolactate synthase, are deployed as broad spectrum and high-efficiency herbicides in order to control the weeds in agriculture. Breeding for rice varieties with resistant to imidazolinone herbicides is one of the economically effective strategies to control weeds in rice fields. In this study, a new rice germplasm resistant to imidazolinone herbicides was identified from 30,570 rice germplasm accessions by spraying imidazolinone herbicides. Testing for resistance in its progeny indicated that this resistance was inheritable. Furthermore, a PCR amplification and sequencing of ALS gene encoding sequence revealed a G/A mutation at position 1880 bp position, which lead to an amino acid alteration from serine (S627) to asparagine (N627) and which might be the causal agent for herbicide resistance. Taken together, this study described an elite germplasm with a practical potential in breeding for new herbicide-resistant rice varieties.