Tooth loss due to extraction could be a big problem, it may cause dysfunction of mastication. The loss of mandibular firstpermanent molar has the highest prevalence. Many cases of tooth loss were not balanced with the prostodontiatreatment. Purpose: The purpose of this research was to determine the relationship between the knowledge level of protheses usage of patients of post extraction mandibular first permanent molar and the usage of protheses at dental polyclinic ofRSUD Ulin Banjarmasin. Methods: This study was used an observational analytic study with cross-sectional design. Samples were taken by purposive sampling technique with 68 patients. Knowledge level was obtained through questionnare. Results: The data were analyzed using chi-square test and obtained value p=0,006. The group with good knowledge level who used protheses were 11 patients (16,1%) and who didn’t used protheses were 20 patients (29,5%). The group with bad knowledge level who used protheses were 3 patients (4,41%) and who didn’t used protheses were 34 patients (37%). Conclusion: There was a relationship between the knowledge level of protheses usage of patients of post extraction mandibular first permanent molar and the usage of prothesis at dental polyclinic of RSUD Ulin Banjarmasin. Keywords: loss of mandibular firstpermanent molar, protheses, knowledge level of protheses usage