<p>This study evaluates the quality of materials in reinforced concrete buildings and their compliance with relevant legislation and earthquake codes. In this scope, field observations of collapsed 400 reinforced concrete (RC) buildings in Kahramanmaraş, Adıyaman, Hatay and Gaziantep provinces, which are among the provinces affected by the Kahramanmaraş earthquakes, were conducted, general information and official documents about the buildings were collected, and detailed investigations including structural material properties were carried out. Some data was obtained from experimental studies conducted in the laboratory. The other part was obtained from reports. Differences were observed in the percentage distribution between the average compressive strength and the minimum compressive strength. In addition, factors such as the use of smooth, large-diameter stream aggregates, inappropriate granulometry, low material quality, poor workmanship, and insufficient compaction negatively impacted the building performance. Additionally, approximately 36% of the buildings were constructed with ribbed reinforcement, 31% with non-ribbed reinforcement, and 25% with both types of reinforcement. The use of ribbed reinforcement in buildings increased significantly after 1997 and its usage rate increased in the subsequent years. The findings of this study will contribute to a better understanding of the current building material deficiencies in earthquake-prone regions and provide information on strategies that should be developed in terms of building materials to improve the resilience of buildings with similar characteristics in other earthquake regions against future seismic events.</p>