A simplified strain-gradient elastoplastic model is developed within the small-strain framework to capture size-dependent mechanical behavior observed at micro and sub-micro scales. The formulation extends classical J₂ plasticity by incorporating both elastic and plastic strain gradients and introducing an intrinsic material length-scale parameter. Under the elastic deformation condition, stresses and their gradients are derived from a strain-energy density, including quadratic contributions from the gradients of the elastic strain. The plastic flow rules are obtained from a dissipation potential formulated in terms of plastic strain rates and their gradients, leading to the emergence of higher-order stresses (double stresses). The model is physically consistent by ensuring nonnegative dissipation. The resulting constitutive relations can be written in a non-incremental form for the total stress, strain, strain gradient, and double stress fields, employing an effective secant shear modulus that captures the interaction between elastoplastic strains and gradient effects. For efficient numerical implementation, the mixed finite-element formulation originally developed for strain-gradient elasticity [1, 2] – where displacement, strains, stresses, and their gradients are treated as independent variables – is extended to strain-gradient elastoplasticity. This extension reduces the continuity requirements to C⁰ finite elements and avoids higher-order interpolation. A multi-level iterative procedure solves the resulting nonlinear problem. The model's predictive capabilities are demonstrated through analysis of a notched plate subjected to uniaxial tension. The results reveal pronounced size effects, including reduced notch opening, elevated stress levels near the notch tip, and sensitivity to both the material length-scale parameter and the notch geometry. The proposed framework captures boundary-layer phenomena and shows good agreement with established strain-gradient theories.