The influence of content and plasticity of fines in sands on field liquefaction assessment remains still somewhat unclear in geotechnical practice. In field liquefaction assessment, corrected standard penetration number (N-1)(60) or cone penetration resistance (q(c)) were used in general to evaluate the liquefaction resistance of sands with fines. (N-1)(60) or q(c) are generally related to the relative density of sands. In this study, stress-controlled cyclic simple shear tests were performed on sands with up to 10% plastic and non-plastic fines at different relative densities. The results demonstrated that at the same relative densities, sands with fines (up to 10 % content) have lower liquefaction resistance than clean sands. Furthermore, the effect of plasticity and the content of fines diminishes at loose states of sand specimens with low fines content. In sands with plastic clays, the relative density has less effect on liquefaction resistance when the content of fines increases from 5% to 10% when compared with sands with non-plastic silt. To conclude, further research is needed to correlate these experimental findings to the field liquefaction assessment of sands with fines.