Steel slag is cubical in shape with a high angle of internal friction and high aggregate interlocking characteristics. The material has the potential for use as railway ballast. It is important to make sure several key performances in field to convince the railway agencies for further application. Aggregate impact value and Los angeles abrasion ratio of steel slag were tested. The lateral resistance, electricity resistance, and dynamic displacements under moving trains were also measured on test track. The material tests concluded that steel slag had higher aggregate impact value and lower Los angles abrasion ratios regardless the mix proportion with natural aggregate. As for the overall performance on test track, it was found that the electricity resistance of steel slag was comparable to natural aggregate and will not affect function of track circuit. Steel slag provided significantly higher lateral resistance than regular ballast with natural aggregate. The dynamic displacement under moving train also justified the appropriateness of applying steel slag in railway ballast.