In this paper Brownian diffusion of spherical particles near a deformable fluid interface was examined by considering interface deformations that were caused by impulsive motions of the Brownian particles. First, the velocity fields were constructed in terms of eigenfunctions on the bipolar coordinate system which facilitated the separation of variables. Then, the rate of interface deformation was determined to calculate the force acting on a Brownian sphere due to the interface relaxation back toward a flat configuration. In addition, the covariance function of velocity correlation was detemined by solving the Langevin equation which included the effects of the interface relaxation. Finally, the diffusion coefficient of spherical particles was evaluated by utilizing the Einstein-Smoluchowski relation in conjunction with the particle mobility calculated in the presence of a deforming interface.