The present study aimed to evaluate the filling quality of a bioceramic sealer with a single gutta-percha cone technique using ultrasonic sealer activation. Twenty-four single-rooted mandibular premolars were selected. Canals were instrumented and allocated into three groups randomly according to the method of ultrasonic sealer activation: group 1: single-cone with ultrasonic activation, group 2: single-cone with Vibration Thermo-hydrodynamic obturation (Vibra THO) technique, group 3: single-cone without ultrasonic activation. After setting of sealer, teeth were immersed in methylene blue dye then demineralized and cleared. Microleakage was assessed under stereomicroscope at 20x magnification. ANOVA and Bonferroni post hoc tests were used for the evaluation of dye penetration at the apical three mm of the roots. Single-cone without ultrasonic activation had the highest mean value of apical microleakage (4080.2±1132.1 μm) followed by the Vibra THO technique (2033.3±1754.3 μm) and the least results with single-cone with ultrasonic activation (1389.1±1094.8 μm) with statistically significant difference between the groups (P<0.05). In multiple comparisons, only statistical significant difference was found between single-cone without ultrasonic vibration and single-cone with ultrasonic activation. It was concluded that when using premixed bioceramic sealer with SC, ultrasonic activation is recommended to obtain better sealing ability of the canals.