Aim: The aim of the study was to assess the post space volume change after the removal of the fiber post from endodontically treated teeth by ultrasonic and by the Er,Cr:YSGG laser and compare between them using cone-beam computed tomography (CBCT). Materials and Methods: This study used twenty-four extracted human single rooted teeth. They were mechanically prepared after their crowns were cut off near the cemento-enamel junction (CEJ). All roots were obturated with gutta-percha points and resin-based sealer. The post space preparation was made to all roots to receive the glass fiber posts. The post space volume was measured by CBCT before post cementation. The roots were divided into two groups (each = 12) according to the technique used in post removal. Group A: ultrasonic. Group B: Er,Cr:YSGG laser. CBCT was used to measure the post space volume after post removal. The difference between before post cementation and after post removal (dentin volume loss) was calculated, and the results were statistically analyzed. Results: In all groups, the post space volume after post removal was significantly higher than the post space volume before post cementation. Group B had a significantly higher mean value of dentin volume loss than group A. Conclusions: The post space volume after fiber post removal by the Er,Cr:YSGG laser or by ultrasonic was significantly higher than before post cementation. The use of the Er,Cr:YSGG laser in fiber post removal produced more dentin volume loss than ultrasonic.