The Design-Build delivery method has gained popularity in the construction industry in the 21st century among clients seeking singular responsibility, shorter delivery time frame and management of complex works. In this exploratory study, a model that considers the effects of project technical system on the project organisation structure has been proposed. Project technical system comprises of two dimensions: technical uncertainty and technical complexity, while integration, organisational differentiation, information processing and project size were considered as dimensions of the project organisation structure. Several hypotheses linking the relationship between technical uncertainty, technical complexity and project structure has been developed. A self-administered questionnaire was developed as the data collection instrument. Field data were collected from design-build projects in the civil and architectural construction industry in Taiwan, and analysed at the project level. The technical system-structure relationships were tested statistically mainly by multiple regression. Results indicate that various scholarly perspectives of uncertainty have a common underlying construct. Several inter-correlations among components of the technical system were identified, and interactively they affect the project organisation structure. Technical uncertainty was found to be a better predictor of information processing and internal integrative efforts than technical complexity. Less structured and flexible information processes and coordinative mechanisms were favoured under high levels of technical uncertainty and complexity. Technical complexity was found to partially predict organisational differentiation, particularly by the interacting effects of project scope and concurrency. The level of technical staffing could be explained by project scope and technical differentiation of the complexity dimension. Lastly, the results were mixed for technical complexity as a predictor of the extent to which project work is subcontracted. The findings of this study contributed to the understanding of the relationships between technical system and organisation structure in complex Design-Build projects. Various managerial implications were outlined. The model proposed in this study can be extended to include project effectiveness, which may lead to the identification of key structural arrangements that contribute to improved project performance.