Experimental and numerical investigations of aluminium alloy square hollow sections with a circular hole in the webs subjected to web crippling are presented in this paper. A total of 216 data that include 84 test results and 132 numerical results are presented. The web crippling tests were conducted under two loading conditions of end-two-flange (ETF) and interior-two-flange (ITF). The test specimens were fabricated by extrusion using a 6061-T6 heat-treated aluminum alloy. The web holes were located at the mid-depth of the webs and centred beneath the bearing plates. A non-linear finite element model is developed and verified against the experimental results. Geometric and material non-linearities were included in the finite element model. It was shown that the finite element model closely predicted the web crippling strengths and the failure modes of the tested specimens. Hence, the model was used for an extensive parametric study of the different sizes of the cross-section and circular holes in the webs. The influence of the circular web holes on the web crippling strength of aluminium square hollow sections is investigated in this study. Web crippling strength reduction factor equations are proposed for the ETF and ITF loading conditions. It is shown that the proposed strength reduction factors are generally conservative and agree well with the experimental and numerical results. Furthermore, a unified web crippling equation for the aluminium square hollow sections with circular web holes is also proposed.