The structural and magnetic properties of the Al-doped La0.75Sr0.25Mn0.5Cr0.5-xAlxO3-delta (x = 0.0, 0.1, 0.2, 0.3) were investigated by X-ray powder diffraction, neutron powder diffraction and magnetization measurements. Rietveld refinement of the diffraction data confirms that the compounds crystallize in rhombohedral symmetry (space group, R-3C). Unit cell volume decreases with increasing concentration of Al at the B-site. Upon cooling from room temperature, we have observed multiple magnetic phase transitions, i.e. paramagnetic (PM), ferromagnetic (FM), antiferromagnetic (AFM) and spin-glass (SG), in the samples. A low temperature magnetic hysteresis study demonstrates the presence of ferromagnetic domains for all compositions. The antiferromagnetic transition temperature decreases with the Al-doping ac susceptibility measurements at 97 Hz and 1 Oe show SG behaviors with a spin-freezing temperature close to 50 K for all samples. The in-phase ac susceptibility (chi') decreases in magnitude and spin-glass transition (T-SG) increase toward higher temperature with increasing frequency. The spin-glass behavior accompanied by the anomalous magnetic transitions is due to the competing interactions between FM and AFM. The results also shows that a part of the samples lose magnetic order to form a SG state accompanied by an AFM state at low temperature. (C) 2013 Elsevier Ltd. All rights reserved.