Objectives : This study aims to elucidate the rational dimensions of Huangdi Neijing, a foundational text of ancient Chinese medicine. Methods : A qualitative textual analysis was conducted on key chapters of Huangdi Neijing, including Suwen and Lingshu. The study identified six dimensions of rationality-worldview of nature as cosmos, disenchantment, theoretical rationality, practical rationality, comprehensive systematization, and lifestyle rationalization-through a philological approach. To minimize bias, the analysis focused on primary texts while excluding secondary interpretive frameworks. Comparative analysis with contemporaneous texts was avoided to emphasize Neijing's intrinsic rationality. Results : The analysis demonstrated how Huangdi Neijing constructs a rational medical system. The worldview of nature as cosmos serves as the foundation for all rationalities by enabling rational understanding of, prediction of, and practice in relation to nature, humanity, and disease. Disenchantment is evident in its rejection of magic and supernatural elements such as gods, spirits, and ghosts. Theoretical rationality manifests in abstract concepts (e.g., nourishing qi, protecting qi, exterior and interior, root and tip) and frameworks (e.g., disease etiology, lifecycle theory). Practical rationality is demonstrated through examples such as treatments based on environmental and lifestyle factors and practical concepts used in pulse diagnostics. The text's comprehensive systematization integrates anatomy, pathology, diagnostics, and regimen. This reflects the effort to rationalize medicine as a discipline. Lifestyle rationalization organizes daily life (e.g., sleep, physical activity, dress, ethical attitude) according to seasonal changes, extending health management beyond the limitations of treatment. Conclusions : These features evident in the Neijing indicate that its medical system is fundamentally rational. Traditional scholarly emphasis on correlative thinking requires reexamination in light of these rational dimensions.