Aim: The aim of this study was to compare the cleaning ability of a single file system (OneShape) versus multi-file systems (ProTaper Universal & ProTaper Next) in curved root canals. Materials and methods: Sixty mesiobuccal roots from extracted mandibular molars were divided into three groups (n = 20): PTU, prepared by ProTaper Universal system; PTN, prepared by ProTaper Next system; and OS, prepared by OneShape system. Teeth were longitudinally split into two halves for evaluation by stereomicroscope. Digitised images were analysed using ImageJ Software for the amount of debris along the canal walls. Results: No significant difference was found between the three groups in the coronal third of the canals (P = 0.17). However, the OneShape group recorded a significantly higher percentage of debris in the middle and apical thirds (P = 0.003 and P = 0.023, respectively) Conclusions: The single-file system showed relatively decreased cleaning ability in curved canals when compared to the use of rotary full-sequence NiTi systems. Keywords: cleaning ability, OneShape, ProTaper Next, single file