We have studied the electronic structure and investigated the synthesis conditions to optimize the superconducting properties of the binary carbide La2C3. From the electronic structure calculation based on two different reported crystal structure determinations, the Fermi level (E-F) is found to be located near a local minimum of the density of state (DOS) and the DOS at EF varies with a slight change of the structural parameters. These results are consistent with the fact that the superconducting properties of La2C3 are sensitive to the preparation conditions and the annealing procedure. By a careful control of the C deficiency we have improved the superconducting properties and prepare samples showing a sharp superconducting transition of T-c = 13.2-13.3 K. Critical fields, H-c2 (7) estimated from resistivity and susceptibility measurement are considerably higher than reported previously. (c) 2005 Elsevier B.V. All rights reserved.