The performance improvement of disk- shaped bulk MgB2 superconductor by means of a nanoscopic diamond powder have been investigated in our previous studies, using a single-step solid-state reaction process. To further improve the critical current density (Jc), we added Ag with varied compositions of 3.5, 4.0, 4.5 wt.% in the optimized composition of 0.8 wt.% of nanodiamond added MgB2 sample and synthesized in pure Ar atmosphere. All samples were sintered at an optimized temperature of 775°C for 3 hours. X-ray diffraction patterns conformed to the main phases of MgB2 samples with additional phases observed in the Ag-added samples. Microstructures were observed with high magnification in field emission scanning electron microscope (FE-SEM) and indicated AgMg nanoparticles are embedded in the MgB2-nanodiamond matrix, which was correlated with XRD studies. Among, the 4.0 wt.% Ag doped sample exhibited the highest Jc of 389 kA/cm2 at 20 K. The present result showed that Ag addition to MgB2-nanodiamond is an effective pinning medium for bulk MgB2 and might thus be attractive for a further performance improvement of the bulk MgB2 material.