Abstract: An integral equation method is proposed for analyzing the pile groups under lateral loading. The interaction problem between two piles is formulated by decomposing the pile soil system into an extended elastic soil and fictitious piles. According to the displacement compatibility condition, a Fredholm integral equation of the second kind is established and solved by using Matlab software. The present approach extends the interaction factor solutions proposed by Chen & Chen (2008) to the more practical case of fixed-head laterally loaded piles, and its accuracy and applicability are validated by means of the existing solutions. Numerical results for two fixed-head laterally loaded piles show that the displacement interaction factors decrease as pile spacing and departure angle increase, but increase with increasing pile-soil slenderness. Based on the interaction factor solutions, the present method can be applied to the responses of fixed-angle pile groups subjected to lateral loading .