Shear tests were carried out on interface between two concrete eco-blocks which comprise segmental retaining wall. Three interface conditions were considered : 1) direct contact of two blocks, 2) placing rubber pad between two blocks, 3) placing rubber pad and shear key between two blocks. According to shear tests, shear load-shear displacement relationship which was obtained from direct contact of two blocks was similar to elastic-perfectly plastic behavior. Ductile behavior of shear load-shear displacement relationship was observed for the interface condition of placing rubber pad. Apparent minimum shear capacities and apparent friction angles for the interface conditions of direct contact of two blocks, placing rubber pad between two blocks, placing rubber pad and shear key were 1.7 kN/m, $27.6^{circ}$ and 4.2 kN/m, $26.2^{circ}$ and 20.9 kN/m, $26.0^{circ}$ respectively.