Single-staged consolidated drained direct shear tests are carried out on a re-compacted completely decomposed granite (CDG) soil, a typical residual soil in Hong Kong, under different matric suctions. Pore-air pressure and pore-water pressure are controlled by applying axis-translation technique. The experimental results show that no soil dilatancy is observed for zero matric suction (saturated case) but as the suction value is increased higher soil dilatancy is obvious. The dilation angle increases with matric suction and the rate of increment is higher in lower suction range than higher suction range. The contribution of suction to shear strength is significant. Shear strength of CDG soil increases with matric suction. The increase in shear strength due to an increase in matric suction (suction envelope) is observed as non-linear.