A rater-blinded randomized controlled trial with a parallel-group design is utilized, comprised of yoga-based group intervention (YoGI) in the experimental condition, and treatment as usual (TAU) in the control condition. The participants in the experimental condition participate in YoGI beside their regular psychiatric treatment (TAU). The intervention is designed for in-patients with schizophrenia spectrum disorders. With the aim of examining the feasibility, acceptability and effectiveness, self-report and blinded rater-based assessments are evaluated before the YoGI (T0), and after four weeks of taking part in intervention (T1). Building on the results of the feasibility and acceptability trial, the study is now progressing to a full randomized controlled trial. The primary outcome for the full trial will be positive symptoms of schizophrenia spectrum disorders, assessed by a blinded rater using the Positive and Negative Syndrome Scale (PANSS). The target sample size has been adjusted to ensure sufficient statistical power, and the trial will evaluate secondary outcomes, including (body) mindfulness, negative symptoms, cognitive functioning, and quality of life, and stress. This study aims to provide robust evidence for the effectiveness of YoGI in comparison to treatment as usual (TAU).