This article examines the magnitude and duration of the effect of the Goods and Services Tax (GST) on inflation in Australia’s eight capital cities using the Box and Tiao intervention analysis and quarterly data spanning from 1948:4 to 2003:1. We found that the GST had a significant but transitory impact on inflation only in the September quarter of 2000 when this new tax system was implemented. In this quarter inflation showed an additional increase of 2.6 per cent in Sydney (minimum effect) and 2.8 per cent in Australia as a whole, and the figure for Hobart was 3.3 per cent (maximum effect). Based on Wald test results, we also found some evidence that there is no significant (or substantial) difference in the average price changes among capital cities. We could not reject the null hypothesis that the GST increased the consumer price index by 2.8 per cent across the board in various cities. These results are also consistent with previous studies and surveys.