The mechanical strength and failure behavior of two photonic crystal silica optical fibers with different diameters were investigated using tensile test. The effect of polymer coating on the failure behavior was also studied. The results indicated that all fibers failed in a brittle manner and the failure normally initiated from fiber surfaces. The failure loads observed in the coated fibers are higher than that in bare fibers and the reason is explained by the apparent delamination between the fiber and the polymer coating when loaded on the fiber surfaces. The relationship between a characteristic parameter measured on the fracture surfaces and the failure stress was examined.