Superconduction YBa₂Cu₃0_(7-x)./Ag composite thick films on a YSZ substrate were prepared by the screen printing method. Microstructure and supercduction properties such as zero-resistance Tc(Tc^(Zero)), Jc at 77k, and the interface reactions betwean the superconduction thick film and YSZ substrate were investigated. For the YBa₂Cu₃O_(7-x)/Ag composite thick films annealed at 980℃ and 1000℃ in flowing oxygen, Tc^(Zero) and Jc at 77k increased, and the normal state resistivity and the thickness of interface reaction layer decreased strongly with increasing Ag content. The drastic decrease in reaction layer thickness with Ag addition seemed to result from the prevention of interaction between the film and the substrate by liquid Ag which formed during high temperature annealing. SEM analysis showed that the grain size increased as Ag content increased from 7wt% to 24wt%. It seems that the liquid Ag in YBa₂Cu₃O_(7-x)/Ag composite thick films enhances the intergranular coupling of YBa₂Cu_O_(7-x)/Ag grains, which results in the favored sintering process at 980℃.