MedReason is a comprehensive medical reasoning dataset that enhances large language models (LLMs) by utilizing a structured medical knowledge graph to create detailed reasoning paths from clinical question-answer pairs. The dataset includes 32,682 QA pairs with step-by-step explanations, and the MedReason-8B model, fine-tuned on this data, achieves state-of-the-art performance in medical reasoning tasks. The project is open-sourced, providing access to models, data, and deployment codes for further research and applications.