In this paper, an elliptical multi-antennas resonating at 3.5 GHz for possible MIMO (Multiple-Input Multiple-Output) mobile communication system is presented. Firstly, the antenna unit was designed and simulated to be operating at this frequency. Then, a defected ground structure (DGS) technique was used in the designing of multi-antennas to allow good isolation and reduce the mutual coupling between them. Simulated results show that, over the entire frequency band of interest, the proposed configuration could attain low correlations between antennas with only defected ground structure technique. Compared to multi-antennas without this technique of isolation, the proposed structure reduces the coupling with 10 dB at 3.5 GHz.