Background. Mean platelet volume (MPV) is an inexpensive, routinely measured clinical parameter, and its elevation shows an increase in the size and activity of platelets. It has been shown that MPV can be used as a prognostic biomarker in certain chronic diseases. In the present study, MPV in patients with hepatitis B virus-related decompensated cirrhosis (HBV-DeCi) was investigated to evaluate whether MPV may have utility as a new predictive marker for mortality in HBV-DeCi patients. Methods. This was a retrospective cohort study that included 120 patients with HBV-DeCi. Results. MPV levels were observed to be significantly higher in the non-surviving patients compared to the surviving patients. The results of a multivariate analysis suggest that both MPV and the model for end-stage liver disease score are independent predictors of 3-month mortality in HBV-DeCi patients (P<0.01). Conclusions. The present study supports that high MPV can be considered as an independent biomarker for predicting 3-month mortality in patients with HBV-DeCi.