One of the important factors aecting the quality of concrete is the placement of fresh concrete inside the formwork. Inadequate compaction is a common problem in concrete technology. In this study, the eect of inadequate compaction on compressive strength and ultrasonic pulse velocity of concrete exposed to elevated temperature is examined. For this purpose, various compaction rates were applied during the casting stage of concrete in order to simulate various levels of inadequate  compaction. Four dierent water-cement ratios (0.50, 0.40, 0.38, and 0.35) were selected. All concrete specimens were exposed to 450 or 900C for one hour. The Taguchi approach was used to reduce the number of samples. The results were evaluated by the Analysis of Variance (ANOVA) method. Test results showed that inadequate compaction played a signicant role, more than curing time, in the compressive strength after high temperature exposure.