A series of drop-weight tests have been carried out to investigate the enforcing effect of steel fibres on impact resistance of lightweight-aggregate concrete (LWC) with the drop weight test method recommended by the American Concrete Institute (ACI) Committee 544. The tested specimens were prepared as discs with size of 152 × 64 mm and five levels of volume fraction of steel fibres as 0·0%, 0·5%, 1·0%, 1·5% and 2·0% respectively. The experimental results show that the impact resistance of LWC—that is, the number of blows to first visible crack as well as to failure—can be greatly improved by including steel fibres. Moreover, it is observed that with higher volume addition, a greater improvement of impact resistance will be achieved. In view of the variation in impact resistance test results, the two-parameter Weibull distribution was adopted to analyse the test data. It is proved that the probabilistic distribution of the blows to first crack and to failure of steel-fibre-reinforced lightweight-aggregate concrete (SFLWC) can be modelled well by two-parameter Weibull distribution. Lastly, the impact resistance formulae for SFLWC with each steel fibres addition are developed to facilitate the application.