Low Electromagnetic Field (EMF) intensity in the range of $1{mu}T;to;10{mu}T$(Tesla) was found to enhance the growth of CHO cells and the production of tPA in batch and perfusion cultivations. At $1{mu}T;intensity,;1.3{ imes}10^7$ viable cells/ml of maximum cell density and 80 mg/l of maximum tPA production were obtained in batch cultivation, compared to $2.8{ imes}10^6$ viable cells/ml and 59 mg tPA/1 in unexposed case (control). A similar trend was observed in the perfusion process, where it was possible to obtain $1.2{ imes}10^7$ viable cells/ml of maximum cell density and 81 mg tPA/l of maximum tPA production by more than 80 days of cultivation. However, there was not much difference between $1{mu}T;and;10{mu}T$ in perfusion cultivation, possibly due to better environmental growth conditions being maintained by continuous feeding of fresh medium into the reactor. On the contrary, both cell growth and tPA production were severely inhibited at higher than 1 mT intensity, showing no growth at 10 mT exposure. Specific growth rate was linearly correlated to specific tPA production rate at $1{mu}T$EMF intensity, which represents a partially growth-related relationship. It was also found that a large amount of $Ca^2+$ was released at low EMF intensity, even though the cell growth was not much affected. Low EMF intensity significantly improved both cell growth and tPA production, and tPA production seemed to be more affected than the cell growth, possibly due to the changes of cell membrane characteristics. It can be concluded that the elaboration of EMF intensity less than $10{mu}T$ could improve cell growth and tPA production, but mainly tPA secretion through batch or perfusion process in a bioreactor.