Based on the well-known Debye-Huckel approximation and the Dejaguin's integration method, this paper presents an integral solution for the electrical double-layer (EDL) interaction between a spherical particle and a cylinder The effects of the relative dimensions of the cylinder to the sphere on the EDL interaction are studied using this numerical solution. The detailed numerical results indicate that, in general, the curvature effect on the EDL interaction cannot be neglected at small separation distances. The widely used sphere-flat plate approximation will considerably overestimate the actual EDL interaction between a spherical particle and a cylinder. The ratio of the radius of the particle to the EDL thickness, tau = kappaa(p), also plays an important role in determining the EDL interaction at small dimensionless separation distances (less than or equal to3 tau (-1)). In addition, it is found that at small separation distances, the EDL interaction can become attractive between two asymmetric EDLs, even though their zeta potentials have the same polarity.