The kinetics of hybridoma cells secreting monoclonal antibodies against hCG (human Chorionic Gonadotropin) were studied comparatively in batch and dual hollow fiber bio-reactors. The oxygen uptake rate of the hybridoma cells was measured in a spinner flask. It went through the peak value of 11.0 $\mu$g $O_2/10^6$ cells-hr during the exponential growth phase. pure oxygen inhibited cell growth. The dual hollow fiber bio-reactors were designed such that oxygen can be supplied through the silicone membrane containing two or three microporous polypropylene hollow fibers. The cells grown in dual hollow fiber bio-reactors lived longer than in a hollow fiber bio-reactor with external silicone aeration circuit. In the batch reactors specific monoclonal antibody production rate corresponded well with that of glucose consumption. Teh final cell density in the dual hollow fiber bio-reactors were estimated to be $0.5-1.0\times10^8$ cells/ml, which was 100 times higher than that in the batch system.