A bstract An angular analysis of the decay B d 0 → K ∗ μ + μ − is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb −1 of integrated luminosity collected during 2012 at centre-of-mass energy of $$ \sqrt{s}=8 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo>=</mml:mo><mml:mn>8</mml:mn></mml:math> TeV. Measurements of the K * longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.