The present study investigates the role of titanium in grain refinement of Mg–3Al and Mg–9Al alloys. Minor amount of Ti addition (<1 wt% of Al–Ti master alloy) brings about grain refinement in both Mg–3Al and Mg–9Al alloys. Ultrasonic treatment further improves the grain size reduction in Ti added Mg–Al alloys. The average grain size of Mg–Al alloys are reduced by 20–30 % from the non-refined alloy by the addition of 1 wt% of Al–Ti master alloy and ultrasonic treatment further enhances the grain refinement by 10–20 %. In addition, ultrasonic treatment transforms the network type β-Mg17Al12 phase into fine discontinuous precipitates in Ti containing Mg–9Al alloys. The mechanism of grain refinement in ultrasonic treated Ti containing Mg–Al alloy is discussed in terms of solute and heterogeneous nucleation perspective. © 2015, The Indian Institute of Metals - IIM.