Fine carbon fibers having a fiber diameter of 1 m or less, an interlayer distance d₀₀₂ between carbon layers as determined by an X-ray diffraction method of 0.335 to 0.342 nm or less and satisfying d₀₀₂<0.3448-0.0028 (log ) where stands for the diameter of the carbon fibers, and a thickness Lc of the crystal in the C axis direction of 40 nm or less. Fine carbon fibers containing boron in crystals of the fiber. The fine carbon fibers can be produced by using vapor-grown fine carbon fibers as a raw material, adding a boron or a boron compound to the material; pressing the mixture to regulate the bulk density to preferably 0.05 g/cm³ or more; and heating at a temperature of 2000 C. or higher.