Skin complication caused by anti-programmed cell death-1(PD1)antibody is a typical immune-related adverse event. We designed this study to clarify the correlation between risk factors(patient's background and laboratory data)and skin toxicity( rash and eruption, excluding itch)after administration of either nivolumab or pembrolizumab. From February 2016 to January 2018, we evaluated the clinical outcomes of 54 patients who were administered anti-PD1 antibody. The patients were divided into 2 groups: 9 patients with skin eruption caused by anti-PD1 antibody(skin eruption group)and 45 patients without skin eruption caused by anti-PD1 antibody(non-skin eruption group). Univariate analysis revealed a significant difference in eosinophil counts in both the groups before anti-PD1 antibody administration(>300/µL)(p=0.020). Factors with p<0.2 in the univariate analysis and 4 factors, age(<65 years of age), sex(male), allergy(+), and pembrolizumab, likely to be related to the appearance of skin eruption, were examined by multivariate analysis. Consequently, eosinophil count before anti-PD1 antibody administration(>300/µL)was identified as a risk factor (odds ratio: 9.530, 95% confidence interval: 1.260-71.80). In conclusion, we suggest that cases with an increased eosinophil count before anti-PD1 antibody administration(>300/µL)may be associated with the appearance of skin eruption.