An optical surface edge Bloch mode is an optical state evanescently bound at an edge on a finite-size three-dimensional photonic crystal; the edge is the intersection of two termination planes on the crystal. Low-loss subwavelength-scale edge modes can appear on an <010> edge of a dielectric woodpile within a complete photonic bandgap. The mode area is as small as 0.066 squared half-in-vacuum-wavelengths. The edge mode has field maxima in vacuum near the termination surface, like surface plasmon modes. This edge mode would provide new opportunities of low-loss light localization in a sub-diffraction-limit space without the use of metal.