The aim of this single-center cross-sectional study was to detect the prevalence of selected periodontal pathogenic bacteria and active matrix metalloproteinase-8 (aMMP-8) level in patients before (preLTx) and after liver transplantation (postLTx). Periodontal pocket depth (PPD) and clinical attachment loss (CAL) were assessed. Subgingival biofilm samples were analyzed using polymerase chain reaction (PCR) to detect 11 common periodontal pathogens. Gingival crevicular fluid (GCF) samples were analyzed with enzyme-linked immunosorbent assay (ELISA) to determine aMMP-8 level and assigned to a scoring system: score 0: 0-8 ng/ml, score 1: 8-20 ng/ml, and score 2: >20 ng/ml. The following were used for the statistical analysis: t test, Mann-Whitney U test, Fishers test (alpha = 5 %). In total, 110 patients (preLTx: n = 35, postLTx: n = 75) could be included in the study. Periodontal findings were not significantly different between groups. In microbiological analysis, a significantly higher prevalence of Campylobacter rectus in preLTx group was detected (p = 0.03). Significantly more patients with score 0 in postLTx group (p = 0.024) and significantly more patients with score 1 in preLTx group were found (p = 0.004). Furthermore, aMMP-8 concentrations for patients with moderate periodontitis were significantly lower in postLTx group compared to preLTx group (p = 0.045). Additionally, in postLTx group, aMMP-8 concentration was significantly higher in patients with severe periodontitis compared to those with no/mild periodontitis (p = 0.016). LTx appears to affect aMMP-8 level, but not bacterial findings in patients after LTx. Determination of aMMP-8 level in patients after LTx with immunosuppressive medication might lead to wrong interpretation of the results.