Piled foundations are used in the cases where the structural loads cannot be carried safely with the shallow foundations. Piled raft foundation has become a prominent foundation system in recent years due to that it combines load bearing capacities of piles and raft. Therefore, comprehensive analytical and experimental studies have been carried out for reliable and economic design of piled raft foundations. In this study, the effects of design parameters of piled raft foundations in sand (pile spacing, pile diameter, pile length and relative density etc.) have been investigated experimentally. In the laboratory tests, model composite (steel and concrete) piles with diameters of 20, 30 mm and lengths of 200, 300 mm were used. The raft was made of steel plate with plan dimensions of 160x160, 240x240 mm and a thickness of 6 mm. The model piled raft foundations with different design parameters were tested. From the tests results, as the pile spacing getting larger, the bearing capacities of the model pile raft foundation increased up to a limit value and the optimum distance between the piles was determined to be 4D. Some design parameters are suggested for use in foundation engineering applications.