High-quality, uniform, one-dimensional (1D) lanthanum hexaboride (LaB6) nanostructures with different morphologies (for example, sparse or dense nanoneedles, or nanorods and nanowire arrays) were fabricated through an effective, easily controlled, one-step, catalyst-free chemical vapor deposition process. The morphologies, structures and temperature-dependent field emission (FE) properties were systematically investigated. FE measurements at room temperature (RT) showed that LaB6 nanowire arrays possess the best FE characteristics among all 1D LaB6 nanostructures, with a low turn-on electric field (Eto, 1.82 V μm−1), a low threshold electric field (Ethr, 2.48 V μm−1), a high current (5.66 mA cm−2 at 2.92 V μm−1) and good stability (at a testing time of 1000 min, fluctuations were <6.0%). Temperature-dependent FE showed that the turn-on and threshold electric fields decreased from 1.82 to 1.06 and 2.48 to 1.62 V μm−1, respectively, whereas the emission current density increased significantly from 0.20 to 9.05 mA cm−2 at 2.20 V μm−1 when the temperature was increased from RT to 723 K. The emission current density and the dependence of the effective work function on temperature were also investigated. We attribute the significant reduction of the turn-on and threshold fields and the remarkable increase of emission current to a decrease in the effective work function with temperature.