Abstract: Whether different generations of IBV M41 strain could be used as seed for producing vaccine was evaluated. In this article IBV M41 strain was handed down from 1 to 8 generation. The 3rd, 5th and 7th offsprings were chosen for evaluating their immunogenicity by detection of their EID50. Vaccines to the three generations were prepared and used for inoculating the SPF chicken. The results indicated that the three vaccines could protect the birds and the protection rate was all above 9/10. The controls were infected and showed signs of the disease. The antibody titers of them were assayed at post-inoculation and the results indicated that the mean antibody titer rose to 3 times of that of the pro-inoculation. Different generations of IBV M41 strain still kept good immunogenicity and could be used as product seed for preparing IB vaccines.