While various studies have explored the integration of sustainability in the construction sector of Tanzania, particularly in areas like energy efficiency and green building practices, there remains a significant gap in understanding the specific barriers to the selection of sustainable building materials (SBMs) in residential projects. This research intends to bridge this gap by identifying and analyzing the critical barriers that hinder the effective selection of SBMs in Tanzania's residential building projects. By employing qualitative interviews with experts from regulatory bodies, public developers, and academic researchers, the study provides a comprehensive overview of the barriers. To ensure the collection of relevant and insightful data, the study involved the selection of participants based on specific criteria tailored to each category of experts. To be able to analyze qualitatively the data collected, this study employed Atlas.ti and MS Excel software. The findings revealed six categories of critical barriers affecting the selection of SBMs for residential building projects in Tanzania were identified and analyzed: (1) Regulatory and Policy Barriers (2) Financial Barriers (3) Knowledge and Awareness Barriers (4) Technical Barriers (5) Market and Supply Chain Issues (6) Cultural and Social Barriers. Moreover, the lack of awareness and limited knowledge issue were as equally importantly voiced as regulatory and policy barriers to affect the effective selection of sustainable materials in Tanzania. This study underscores the need for targeted policy interventions that address the lack of awareness, financial difficulties, and the absence of comprehensive regulatory frameworks to promote the selection of sustainable materials.