We investigated the feasibility of a printing technology for Ag circuit formation on a FR4 substrate. A conductive paste containing Ag nanoparticles (73 wt%) of 20-50 nm diameter was screen printed on an FR4 substrate and sintered under a sintering temperature ranging from 100 degrees C to 200 degrees C for 30 min. We carried out the thermal analysis of the Ag nanopaste to confirm the suitability of the set-up conditions. To investigate the sintering degree with various temperatures, fractured cross-sections were observed by field emission scanning electron microscopy (FESEM). For electrical characterization of the printed Ag circuit, a four-point probe method was used to measure the direct current (DC) resistivity, while a network analyzer and Cascade's probe system in the frequency range from 10 MHz to 20 GHz were used to measure the scattering parameters (S-parameter) of the sintered Ag conducting patterns. The resistivity under the application of a DC signal decreased as the temperature increased. The measured S-parameters indicated that the electrical losses decreased as the sintering temperature increased due to the interparticle neck formation after heat treatment at high temperatures.