Stroke, spinal cord injuries, and various traumas often result in hemiplegia, and in such conditions, one of the biggest problems is muscle weakness. As a result of weakened muscles, the problem of foot drop often occurs. Because the patient is unable to perform dorsiflexion, there is an irregular gait pattern - gait speed decreases, the metabolic cost is increased and there is a high risk of tripping. Reduced ability to walk significantly affects the quality of life, which makes walking rehabilitation necessary. Orthotic treatment is most attributed to the treatment of foot drop. The most used ankle-foot orthoses are still passive orthoses. However, advances in technology have led to the increasing development of active orthoses. Significant progress has been made in the development of active ankle-foot orthoses in recent years, but there is still no practical and mobile solution for wider application. Therefore, the goal of this work is to propose a mobile active ankle-foot orthosis. To better understand the problem of foot drop and the needs of users, the anatomy of the lower extremities and the biomechanics of movement was first studied. Then, by reviewing scientific papers, it was observed that there are proposals for active orthoses that meet some of the user's needs. Existing orthoses were analyzed and evaluated, and some of their characteristics were used as a basis for developing own solution. The designed active orthosis in addition to solving the problem of foot drop also can help in the push-off phase and additional stabilization. The advantages of the offered structural solution are the compactness and design, which contribute to the aesthetic value of the product and reduce the aversion of the user to the use of the orthosis. Since innovative solutions were used in parts of the construction, subsequent iterations of the orthosis and experimental testing are proposed.