Fatigue crack propagation behaviour of 2024-T3 aluminium (Al) alloy under periodic overloads superimposed on constant amplitude loadings with R=0.5 and f=10 Hz was investigated by scanning electron microscopy (SEM). During the variable amplitude loading tests for every 1200, 2500 and 5000 cycles, a block of 100 cycles overload was applied. For variable amplitude loading tests, crack propagation rates were lower than in constant amplitude loading tests. Applied periodic overloads have a retardation effect on crack propagation and this effect was greater for 2500 cycles than 1200 and 5000 cycles. In the SEM, the retardation effect of block overloading was clearly observed.