New duck disease caused by Riemerella anatipestifer is a new disease emerged in Kerala from 2008 onwards. Six R. anatipestifer isolates responsible for the disease were isolated from suspected ducks from different outbreak areas of the state and were identifi ed. Since the ecological, morphological and cultural characteristics of R. anatipestifer are more or less similar to Pasteurella multocida, the disease is often confused with duck pasteurellosis and misdiagnosed. R. anatipestifer infection is also characterized by the presence of bipolar organisms in blood smear and impression smears of organs as in the case of P. multocida, but the size is little larger. The detection and identifi cation of the causative bacterium, from ducks with signs and lesions consistent with the acute or chronic form of the disease, is one of the most important aspects of disease diagnosis. Hence, a study was conducted to isolate the agent of new duck disease and stating its differential biotyping characters from that of P. multocida. They were differentiated using tests like indole production, gelatin liquefaction, ornithine decarboxylases utilization and fermentation of glucose. The antibiogram pattern was determined to advocate the choice of drug for the purpose of treatment. All the R. anatipestifer isolates were sensitive to chloramphenicol, ciprofl oxacin, enrofl oxacin, norfl oxacin, gentamicin, clindamycin, doxycycline and cefuroxime.