Percentage of gutta-percha-filled area (PGFA) was used to investigate the sealing ability of GuttaFlow. A total of 80 mandibular first premolars with single canal were randomly divided into 4 Groups (n=20) according to root canal filling technique and/or material - Group1: cold lateral condensation technique; Group 2: continuous wave condensation technique; Group 3: GuttaFlow; Group 4: GuttaFlow and accessory gutta-percha cones without lateral condensation. The PGFA values of Groups 3 and 4 were significantly higher than those of Groups 1 and 2 (p<0.05), but there were no significant differences between Group 3 and Group 4 (p>0.05). It was concluded that GuttaFlow provided superior sealing ability, such that accessory gutta-percha cones became unnecessary when filling root canals with GuttaFlow.