It is well known that the finer particle of cementing material has the more pozzolanic reaction than the coarser particle. This paper investigates the shear properties of geocomposite soil with various particle size of bottom ash. Geocomposite soil (GCS) consists of dredged soil, bottom ash and cement. Three different particle sizes of bottom ash were added into soil mixtures: passing No 4 sieve, No 40 sieve, and No 140 sieve, denoted as BA#4, BA#40, and BA #140, respectively. These bottom ashes with different particle sizes have the same chemical component. Several mixtures were prepared with various contents of bottom ash ranged from 0% to 100% at 50% intervals by the weight of dry dredged soil. In this study several series of direct shear tests were carried out. It is found that the shear strength of the GCS increase with an increase in bottom ash content. The mixture BA#4 has higher internal friction angle value than the mixtures BA#40 and BA#140 due to the interlocking effect and friction resistance between the particles with angular shape of coarse bottom ash. However, cohesion of mixture BA#140 has the higher value than the other mixtures due to higher pozzolanic reaction.