Background: This study aimed to evaluate the efficacy of passive ultrasonic irrigation and XP-Endo Finisher on the cleanliness of canal wall surface after post-space preparation. Methods: Forty endodontically treated mandibular premolar teeth were used. After post-space preparation, the teeth were divided into 4 groups. Irrigation protocols were performed as follows; distilled water as a control group (Group 1), NaOCl/EDTA without any activation (Group 2), NaOCl/EDTA irrigation with passive ultrasonic activation (Group 3), and NaOCl/EDTA irrigation with XP-Endo Finisher (Group 4). The teeth were split and the canal walls were examined with scanning electron microscope under 1000× magnification. The presence of debris was evaluated with 3-point scoring system. For each sample 10 scores were obtained and averaged. The results were statistically analyzed. Results: None of the techniques cleaned the root canal walls completely after post-space preparation. Passive ultrasonic irrigation and XP-Endo Finisher groups demonstrated lower scores than the control and non-activated NaOCl/EDTA groups. The highest results were recorded in the control group. Conclusion: The activation with passive ultrasonic irrigation or XP-Endo Finisher was more effective in cleaning of the root canal walls after post-space preparation.