The acoustic emission (AE) response and mechanical behaviour of two Nextel 440 fibre reinforced aluminium composites were compared. The total cumulative AE events were found to occur in two regions. The first region occurred at smaller strains and had a large exponential rise in events for the reinforced 6061 composite and few events for the high purity aluminium matrix composite. The difference was attributed to the alloy constituents of the 6061 aluminium matrix. The events were attributed to a dislocation release mechanism that occurred prior to yielding of the matrix. In the second region of events in the reinforced 6061 composite the event rate was constant and continued to failure. The second region of events in the high purity aluminium (HPAL) composite had a steady increase in the event rate until a constant rate was reached prior to failure. The events in the reinforced HPAL composite were attributed to the fracturing of fibres and the associated plastic deformation of the matrix that accompanies fibre failure. Thus failure in the materials occurs due to the propagation of fracturing fibres. The propagation was rapid in the reinforced 6061 aluminium composite. The reinforced HPAL composite had a slower propagation due to the high ductility of the HPAL.