The aim of the current study is to clarify the influence of steel cleanliness on the fracture during wet wire drawing of high strength high carbon very fine filaments. Methodologies for inclusion identification and for inclusion count were developed. Ninety percent of the fractured filaments were associated with an inclusion which was SiO2, or SiO2-CaO or SiO2-MgO. The fracture of the wires resulted from debonding of the inclusion from the matrix. Inclusion density assessed from total oxygen content in the wire was successfully and reliably obtained. Inclusions exhibited a wide range of sizes but mostly around 6 μm. The inclusion density did not appear as the only parameter that affects the fracture occurrence. An important effect of size and of chemical composition of the inclusions was found. A critical size of inclusions for fracture was observed but it depends on the chemical composition of inclusions.