The focus of the present paper is to determine the effect of compressibility of the fluid on the stochastic dynamic response of fluid-structure systems by using Lagrangian approach. Variable-number-nodes two-dimensional fluid finite elements were programmed in Fortran language by the authors and incorporated into a general-purpose computer program for stochastic dynamic analysis of solid systems, STOCAL. A two dimensional fluid-structure interaction problem is selected for numerical example. The influence of the compressibility of the fluid is investigated by increasing the value of the bulk modulus of the fluid. Results obtained from Lagrangian approach are compared with each other and those of the Westergaard approach.