The authors have previously reported that welders with high concentrations of welding fumes in their breathing air zone are exposed to dust and Mn if there is leaking air owing to the lack of fitness between respirators and the wearer’s face when using human samples in Japan. The mask fit test confirms whether or not the wearing condition of the wearer’s face and the facepiece of the respirators are used appropriately. The purpose of this study was to investigate whether or not quantitative mask fit test results differed between replaceable and disposable masks. The participants of the mask fit test were 93 male welders in Japan. Replaceable and disposable masks were worn by 85 and eight welders, respectively. In the mask fit test results, the failure rate of the disposable masks was significantly higher than that of replaceable masks. The result may be because the mask did not fit the face or was worn improperly. Masks are the last line of defense to protect welders’ health. Particularly, when using a disposable mask, welders should carefully check whether the mask fits or not.