Petrographic examination technique is one of the well established methods for determining the depth of fire damage in reinforced concrete structure. This paper demonstrates the use of petrography to assess the behavior of concrete structures affected by fire using optical microscopy. Two different types of fire affected buildings were studied by extracting concrete cores and preparing concrete thin samples to study the changes in cement paste, coarse aggregate, fine aggregate, microcracking and other microscopic features to understand the depth of fire penetration inside the concrete. The petrography study revealed that degree of fire damage varies inside the concrete. Findings of the petrographic examination for concrete sample were confirmed with non-destructive test results (mainly with ultrasonic pulse velocity test); loss in the compressive strength and quality of concrete.