In previous works, it was demonstrated that the average fracture-toughness values were higher in the circumferential-longitudinal direction (CL) than in the circumferential-radial direction (CR) on the longitudinal submerged arc welding (SAW) in API 5L pipeline steel. Nevertheless, such differences in fracture-toughness values were attributed to the density distribution of microstructural phases and porosity, but the effect of non-metallic inclusions on this fracture property was not considered; therefore, the present work analyzed the effect of non-metallic inclusions on the fracture-toughness values by fractographic and electron diffraction scattered analyses. The results showed the presence of titanium (Ti), calcium (Ca), and aluminum (Al) constituents in the non-metallic inclusions for the CR direction of the pipeline. These elements tended to form compounds that promoted brittle-fracture by cleavage, decreasing the toughness properties of the weld. For the CL direction analysis, the elements presented on the non-metallic inclusions were manganese (Mn), silicon (Si), and sulfur (S), which promoted the nucleation and coalescence of cavities, all of which were typical for ductile fracture. Calculations on the K_IC showed that the non-metallic inclusions with elements of Ti, Ca, and Al contributed to lower K_IC values on the CR direction under analysis.