Liquefaction phenomenon associated with loss in shear strength of saturated sand is triggered due to monotonically increasing loads or propagation of seismic waves through granular structure under restricted drainage conditions. Such circumstances resulting in excess in pore-water pressure development within a soil-structure result in loss of confinement in soil strata due to decrease in intergranular forces transfer thus leading to strain-softening behaviour of soil matrix. This research focuses on effect of fines content with high plasticity on the liquefaction susceptibility of sand. The study simulates variation in soil composition by incorporating fines of 10, 20 and 30% by dry weight into sand-matrix. Fines are incorporated in three subgroups as silt, clay and equal proportions of silt and clay together to form a Sand-fines matrix. The instability characteristics of test specimen of soil-matrices are evaluated by subjecting them to monotonic and cyclic direct shear box tests and consolidated undrained triaxial tests. The tests specimens are prepared at initial relative densities of 35 % and 70% by dry funnel pluviation technique. Prior to shearing, specimens are consolidated under three different effective stresses of 50, 100 and 150 kPa. The results are analysed based on principles of critical state soil mechanics. The effect of fines addition on the soil fabric is also observed with the use of optical microscope. Amongst all soil groups experimented, Sand and clayey-silty Sand (10%) mixture prepared at loose state exhibited susceptibility for flow liquefaction. Critical state evaluations of all dense specimens indicating the stable response of specimens whilst loose specimens resulting in diverse characteristics. Apropos of loose specimens, liquefaction resistance increases of sand-fines mixture increases up to 20% of fines addition and 30% sand-fines mixtures are plotting in a close proximity of critical state line. Keywords: Critical Void Ratio, Direct Shear Box Test, Fines Separation, Liquefaction, Sand with Fines, Steady State, Triaxial Test