In this study the effect of cyclic loads on monotonic shear strength has been studied on torsional, triaxial and simple shear apparatus. Tests have been conducted on undisturbed fine grained soil specimens. The plasticity index of soils is in the range from NP to 22 for undisturbed soil specimens. The existence of critical shear strain level, which is called as yield shear strain, where softening starts, is determined from cyclic tests. The level of cyclic yield strain is ±0. 5 % for he undisturbed soils. If soil undergoes a cyclic shear strain level below the cyclic yield strain, reduction of monotonic strength of undisturbed specimens is limited but when cyclic shear strain level is larger than yield strain monotonic strength decreases down to 40% of initial strength.