Disclosed is an optical fiber block having holding sub-blocks. The optical fiber block comprises: an optical fiber arrangement section having a V-groove array including a plurality of V-grooves; a stress-relieving recess section extending from the optical fiber arrangement section, the stress-relieving recess section having a flat surface on which a ribbon optical fiber is fixed, the flat surface being formed to be substantially lower than the lower ends of the V-grooves by etching; and at least one holding sub-block formed on a rear portion of the side edge of the flat surface of the stress-relieving recess section, so as to prevent the ribbon optical fiber placed on the flat surface from escaping out of the flat surface and guide the flow of epoxy resin injected toward the ribbon optical fiber.