Summary: The weak Galerkin finite element method (WG-FEM) is a novel numerical method that was first proposed and analyzed by J. Wang and X. Ye [J. Comput. Appl. Math. 241, 103–115 (2013; Zbl 1261.65121)] for general second order elliptic problems on triangular meshes based on a discrete weak gradient. In general, the weak Galerkin finite element formulations for partial differential equations can be derived naturally by replacing usual derivatives by weakly defined derivatives in the corresponding variational forms. The superconvergence in the finite element method is a phenomenon in which the finite element approximation converges to the exact solution at a rate higher than the optimal order error estimate. J. Wang [“A superconvergence analysis for finite element solutions by the least-squares surface fitting on irregular meshes for smooth problems”, J. Math. Study 33, No. 3, 229–243 (2000)] proposed and analyzed superconvergence of the standard Galerkin finite element method by \(L^2\)-projections. The main idea behind the \(L^2\)-projections is to project the finite element solution to another finite element space with a coarse mesh and a higher order of polynomials. The objective of this paper is to establish a general superconvergence result for the weak Galerkin finite element approximations for second order elliptic problem by \(L^2\)-projection methods. The results of numerical experiments show great promise for the robustness, reliability, flexibility and accuracy of superconvergence in WG-FEM by \(L^2\)-projection methods.