Abstract: This paper presents our user and usability studies for applying scenarios in user-centred design to develop a sketching interface for virtual human modelling and animation. In this approach, we utilise the User Centred System Design (UCSD) strategy and spiral lifecycles to ensure system usability and functionalities. A series of usability techniques were employed. After the initial conceptual design, a preliminary user study (including questionnaires and sketching observations) was undertaken to establish the formal interface design. Second, an informal user test was conducted on the first prototype: a 'sketch-based 3D stick figure animation interface'. Finally, a formal user evaluation (including performance tests, sketching observations, and interviews) was carried out on the latest version: a 'sketch-based virtual human builder'. During this iterative process, various paper-based and electronic-based sketching scenarios were created, which were acted-out by users to help designers evoke and verify design ideas, identify users' needs, and test the prototype interfaces in real contexts. Benefiting from applying the UCSD strategy and scenario-based design to develop a natural and supportive sketching interface, our investigation can be a useful instantiation for the design of other sketching interfaces where these techniques have not been widely acknowledged and utilised in the past.