In this study, optimal design of the aluminum electrical railcar under uncertainty of material property is performed. The main structure of the aluminum electrical railcar is composed of aluminum extruded panel. The yield strength and thickness of the aluminum extruded panel are treated as random variables. The loading conditions are based on the standard specification. Stress and resonant frequency are the design constraints and obtained through finite element analysis. The results of reliability-based design optimization considering the uncertainty of material property are compared to those of deterministic optimization.