Milimeter-wave Marchand Balun designed on flat ground and patterned ground shields are presented in this paper. Each of the baluns is designed on top metal (M6) in 0.18μm CMOS technology. In order to achieve sufficient coupling, the balun is stacked on the second highest metal (M5) connected using inter-metal vias. These balun have three port, differential ended port (on top metal) and single ended port (on second highest metal). Patterned ground shield is designed on the ground metal to reduce dielectric substrate loss with strips shield length (SL)=strips shield space(SS)=5μm. The sizes of both designs are 235μm 340μm including pads. It shows that Balun-1 (with flat ground) gave S 11 better than 15dB at 58.02GHz, with ΙS 21Ι and ΙS 31Ι at differential ports, 4.722dB and 5.671dB respectively, while Balun-2 (with pattern ground shields) resulted ΙS 11Ι better than -20dB, with ΙS 21Ι, and ΙS 31Ι of 2.969dB and 4.144dB significantly.