Neutron diffraction and specific heat measurements have been performed to study the magnetic ordering of the Ce ions in the heavy-fermion compound Ce3Al. Detailed crystal structure analysis, determined using high resolution neutron diffraction patterns and Rietveld method, shows that the Ce ions may be grouped into two types: one in the Ce-Al chain, the other in the Ce-Ce chain. The specific-heat data reveal an anomaly at T approximate to 2.2 K, but the calculated magnetic entropy is much smaller than the expected R ln 2 if all Ce spins ordered, Low temperature neutron diffraction measurements confirm that the transition at 2.2 K is magnetic and is associated with the ordering of the Ce spins. The magnetic unit cell is double the nuclear one along the a and c axes, and contains 48 Ce ions, Only the Ce ions in the Ce-Al chains participate in the ordering at 2.2 K, and they are coupled antiferromagnetically. (C) 1998 American Institute of Physics. [S0021-8979(98)21011-5].