Abstract: An additive holder for a PET bottle includes a tubular member having an open top formed with a flange and an open bottom formed with a toothed neck, the tubular member being fitted in the externally threaded mouth with the flange resting on an upper edge of the mouth, the tubular member having an inner side formed with a circular protrusion, a container having an upwardly extending handle and fitted inside the tubular member and kept in place by the circular protrusion, with the handle extending upwardly out of the tubular member, a locking cap provided with internal threaded engageable with the externally threaded mouth and having an axial through hole receiving the handle of the container, and a cover engageable with a top of the locking cap, whereby an additive such as sugar, cream milk, or the like in the container will drop down to mix with a drink in the PET bottle as desired.