Background Granulomatosis with polyangiitis (GPA) is a granulomatous necrotizing vasculitis with high morbidity and mortality. Anti-neutrophil cytoplasmic antibody is a valuable diagnostic marker, however its titer lacks predictive value for the severity of organ involvement. Platelet to lymphocyte ratio (PLR) and mean platelet volume (MPV) has been regarded as a potential marker in assessing systemic inflammation. We aimed to explore the value of PLR and MPV in the assessment of disease activity and manifestations of disease in GPA. Methods 56 newly diagnosed GPA patients and 53 age-sex matched healthy controls were included in this retrospective and cross-sectional study with comparative group. Complete blood count was performed with Backman Coulter automatic analyzer, erythrocyte sedimentation rate (ESR) with Westergen method and C-reactive protein (CRP) levels with nephelometry. The PLR was calculated as the ratio of platelet and lymphocyte counts. Result Compared to control group, ESR, CRP and PLR were significantly higher and MPV significantly lower in GPA patients. In patients group, PLR was positively correlated with ESR and CRP (r = 0.39, p = 0.005 and r = 0.51, p < 0.001, respectively). MPV was negatively correlated with ESR and CRP (r = - 0.31, p = 0.028 and r = - 0.34 p = 0.014, respectively). Patients with renal involvement had significantly higher PLR than patients without renal involvement (median:265.98, IQR:208.79 vs median:180.34 IQR:129.37, p = 0.02). PLR was negatively correlated with glomerular filtration rate (r = - 0.27, p = 0.009). A cut-off level of 204 for PLR had 65.6% sensitivity and 62.5 specificity to predict renal involvement. Conclusion PLR exhibit favorable diagnostic performance in predicting renal involvement in patients with GPA.