Case histories from at least 28 earthquakes worldwide have indicated that liquefaction can occur in gravelly soils (both in natural deposits and manmade reclamations), inducing large ground deformation and causing severe damage to civil infrastructures. However, the evaluation of the liquefaction potential and cyclic strain accumulation characteristics of gravelly soils remains a major challenge in geotechnical earthquake engineering. To provide new and useful insights into this crucial topic, stress-controlled undrained cyclic triaxial tests were conducted on sand-gravel mixtures (SGM) having sand-dominated microstructure but different packing states (i.e., soil grain arrangement), which were obtained by varying the gravel content (GC) and relative density (Dr). The experimental results confirmed that both the GC and Dr have marginal (at low GC and Dr) to significant (at high GC and Dr) effects on the cyclic resistance ratio (CRR) of SGM, but highlighted the need to consider GC and Dr effects together. In this regard, the use of state parameters, such as the equivalent void ratio (ef(eq)) and equivalent relative density (Drf(eq)), were found to be suitable approaches to describe the combined effect of GC and Dr on CRR as they provide unique correlations for sand-dominated SGM irrespective of their packing states.