Abstract: The feasibility of adopting piles with enlarged base for uplift resistance in Shanghai soft soil district has been not well known up to now.To study the uplift behavior of piles with enlarged base,the reasonable base shape and machine for base enlarging were designed.Then full-scale contrast tests on piles with normal straight-shaft and enlarged base were done.The tests were divided into two groups,and there were three piles in each group,one with straight-shaft and the other with enlarged base.The diameter and length of piles in these two groups were different.It indicated that load-settlement curves of piles with enlarged base were flat compared with the steep curves of piles with straight-shaft.With the increase of 5% in concrete material,the uplift capacity of the piles with enlarged base increased 50% more than that of the piles with straight-shafted.Based on the tests,the movement of pile top and toe with increasing loading and rebound rates of pile top and toe after unloading were studied.The full-scale tests verified the effectiveness of uplift resistance of piles with small extend angle in Shanghai soft soil area.The tests were advantageous to the understanding of the bearing mechanism and to the application of such piles with enlarged base.