The seed lectin from Canavalia gladiata was purified and crystallized. Orthorhombic crystals belonging to space group C222(1) grew within three weeks at 293 K using the hanging-drop vapour-diffusion method. Using synchrotron X-ray radiation, a complete structural data set was collected at 2.3 A resolution. The preliminary crystal structure of the lectin, determined by molecular replacement, had a correlation coefficient of 0.569 and an R factor of 0.412.