The effect of calcium on the aggregation and growth of 293 cells grown in either serum-containing or serum-free medium was investigated in T-flask and spinner bottle, respectively. It was found that the concentration of calcium ion, in the range of 0.1 mmol/L to 1.0 mmol/L, affected adhesion and aggregation of 293 cells severely, but had no distinct effect on growth. The result indicated that the attachment of 293 cells was easier with higher calcium concentration in serum-containing medium. And 293 cells formed aggregates readily in suspension culture. This effect was more profound in cultures with higher calcium concentration. The average diameter( D, mum) of 293 cell aggregates exhibited direct proportion to calcium concentration (c, mmol/L) in serum-free medium. It can be depicted by a simple equation in the range of 0.1 mmol/L to 0.5 mmol/L, i.e. D = 58.65c + 16.96. The aggregation size of 293 cells is regulable in suspension culture, therefore, proper control allows for an easier cell retention, and thus a high cell concentration potentially can be achieved. However, similar growth of 293 cells was observed in cultures with different calcium concentration.