This study is focused on experimental evaluation and numerical modeling of micromilling of hardened H13 tool steels. Multiple tool wear tests are performed in a microside cutting condition with 100 μm diameter endmills. The machined surface integrity, part dimension control, size effect, and tool wear progression in micromachining of hardened tool steels are experimentally investigated. A strain gradient plasticity model is developed for micromachining of hardened H13 tool steel. Novel 2D finite element (FE) models are developed in software ABAQUS to simulate the continuous chip formation with varying chip thickness in complete micromilling cycles under two configurations: microslotting and microside cutting. The steady-state cutting temperature is investigated by a heat transfer analysis of multi micromilling cycles. The FE model with the material strain gradient plasticity is validated by comparing the model predictions of the specific cutting forces with the measured data. The FE model results are discussed in chip formation, stress, temperature, and velocity fields to great details. It is shown that the developed FE model is capable of modeling a continuous chip formation in a complete micromilling cycle, including the size effect. It is also shown that the built-up edge in micromachining can be predicted with the FE model.