BACKGROUND This retrospective study from a single center in Poland was undertaken to evaluate the clinical utility of neutrophil-to-platelet ratio in therapy of 35 ulcerative colitis (UC) patients with infliximab or vedolizumab. MATERIAL AND METHODS This study included 35 patients: 16 were treated with infliximab and 19 were treated with vedolizumab. Treatment response was evaluated using partial Mayo score. Treatment response was defined as a reduction of partial Mayo score of ≥3 points followed by a decrease of a minimum of 30% from the baseline, decrease in the rectal bleeding subscore of ≥1, or an absolute rectal bleeding subscore of 0 or 1. During the maintenance period, we diagnosed 13 patients with loss of response (LOR) (5 with infliximab and 8 with vedolizumab). The Mann-Whitney U test was performed to assess differences between the groups. Statistical significance was defined as P<0.05. The median was used to describe the value of the parameter. Analysis of the receiver operating characteristic (ROC) curve with the determination of area under the curve (AUC) was performed for the neutrophil-to-platelet parameter during the induction period. RESULTS The median value of the neutrophil-to-platelet ratio for the treatment response group was lower than in the LOR group (median=13.18 and median=19.49, respectively). Calculation of AUC curve for neutrophil-to-platelet ratio during the induction period showed best sensitivity and specificity for values ≥32.511. There were no other significant findings. CONCLUSIONS Neutrophil-to-platelet ratio might be a promising biomarker of LOR in biologic therapy of UC. However, to fully prove this, further studies are needed.