Study 24 lots of Rotavin-Ml Bulk vaccine on: infected dose, the maintenance medium after innoculation working seed virus on vero cell and the suitable pH of medium. The results show that: (1) The mean titer of infected dose 0.1 FFU/cell give bulk vaccine titer 6.95 Ig FFU/ml and 0.006 FFU/cell show the similar titer 6.91g FFU/ml. So the infected dose on the vero cell with 0.006 FFU/cell and 0.l FFU/cell are not significantly different from each other (P0.05). (2) Using DMEM with 0.0125M Hepes in the maintenance medium is best once, it shows pH of medium more stability at 7.07.15 to abtain high titer of bulk vaccine (7.19 - 7.69IgFFU/ml). (3) Virus grow in static culture and shaking culture to give similar titer. Mean titer are 6.8 and 7.03 IgFFU/ml respectively, they show not significantly different with P0.05. Polyvac has been applied the results for Rotavin-Ml vaccine production in large scale and achieved high titer in bulk material.