Ground penetrating radar (GPR) can be used to locate interfaces and underground utilities, and evaluate ballast fouling conditions, moisture content and subgrade conditions depending on frequencies of antenna and data processing techniques. In Australia, trial testing on railway sections has been conducted by the railway industry. However, in these trials, testing is only conducted on actual tracks where the relationship between track conditions and the GPR response has not yet been established. In this paper, a full scale model rail track designed and constructed at the University of Wollongong is used to investigate factors that infl uence the GPR data quality, such as the GPR antenna frequency, the degree and moisture content of ballast fouling and sampling frequency. GPR testing was conducted using ground coupled antennas with different frequencies. Comparisons are made to identify the suitable frequency applicable for the assessment of track condition which will be used subsequently to improve the accuracy of site investigations.