Inhibition of β-site amyloid–β-protein precursor cleaving enzyme 1 (BACE1) represents a promising approach for the treatment of Alzheimer's disease (AD). However, the development of a selective BACE1 inhibitor is difficult due to its highly flexible catalytic site and homology to other aspartic proteases, including BACE2 and Cathepsin D (CTSD). Aiming to better understand the structural factors responsible for selective BACE1 inhibition, we performed alignment studies, molecular dynamics (MD) simulations and docking studies to explore the recognition of four selective BACE1 inhibitors by aspartyl proteases. The results show that selective BACE1 inhibition may be due to the formation of strong electrostatic interactions with Asp32 and Asp228 and a large number of hydrogen bonds, π-π and Van der Waals interactions with the amino acid residues located inside the catalytic cavity, which has different volume and shape compared to BACE2 and CTSD. Hindrance effects avoid the accommodation of ligands in the small catalytic site of BACE2, resulting in a lower affinity and the high cavity of CTSD results in the formation of a small number of interactions with the ligands, although they show a similar binding mode with BACE1. These results might help to rationalize the design of selective BACE1 inhibitors. •In silico studies showed structural differences between BACE1, BACE2 and CTSD.•The principal structural differences on the catalytic cavity is the volume.•Ligand recognition of four selective BACE1 inhibitors were studied.•The BACE1 selectivity is explained by strong electrostatic with Asp32 and Asp228.