Abstract: An optical fiber coupler comprising a cylindrical fiber holder made of plastics, having a through bore of a size just capable of receiving an optical fiber to be connected and having a portion divided along the through bore in the middle range; a pair of flexible conical collars each of which is engaged with the end portion of the fiber holder and has a bore aligned with the through bore and a slit extending in the lengthwise direction; a cylindrical sleeve fitted on the cylindrical fiber holder to cover the fiber holder and having screw portions at both ends; and a pair of caps each of which is screwed with screw portion of the sleeve to grasp the optical fiber portion passing through the collar with the collar; and an opening aligned with the bore on its end wall, in order to enable to simplify the structure, to make small the entire size, to manufacture at a low cost and to assemble within a short time.