This paper presents the results of research conducted to investigate the effect of the sample size on the resilient modulus of cohesive soils as determined by the repeated load triaxial test. Soil samples from three different sites within the State of Wisconsin were collected and then subjected to standard laboratory tests to evaluate their properties. Soil specimens of 35.6, 71, and 101.6 mm diameter (with length to diameter aspect ratio of 2:1) were prepared according to the standard procedure described by AASHTO T 307 and then were subjected to repeated load triaxial test to determine their resilient modulus values. Test results showed that the specimen size has a significant influence on the resilient modulus of the investigated cohesive soils. Soil specimens with 35.6 mm diameter exhibited the highest resilient modulus values while the specimens with 101.6 mm diameter exhibited the lowest values. The resilient modulus variation with specimen diameter was significant at low deviator stress levels and decreased with the increase of the deviator stress.