The age-hardening behavior and the mechanism of an experimental low gold content casting Ag-Pd alloy were studied by means of hardness test, XRD, SEM and EPMA, The results show that the hardness of specimens isothermal-aged at 400 oC after solution treated at 900 oC for 30 min increases unidirectionally from 1540 MPa to 3160 MPa with the prolongation of time. However, the hardness of the specimens isothermal-aged at 600 oC after solution treated at 900 oC for 30 min increases quickly and reaches the maximun 2870 MPa at 2 min aging time. Then the hardness decreases unidirectionally and remains at 1600-1700 MPa from 10 to 50 min aging time. Obvious precipitation takes place in the specimens isothermal-aged at 400 and 600 oC revealed by XRD. By SEM and EPMA, the precipitation particles can be seen in the specimens aged at 600 oC for 2 min after solution treated at 900 oC for 30 min. However, the time-FWMH curve shows that the increase of hardness after isothermal-aging is closely related with coherency stain from phase transformation. It is hard to define whether the phase transformation at 400 oC makes a contribution to the change of hardness