The present invention relates to a coupler assembly for a tibial cutting guide, the assembly including an aligning coupler having a first side coupled to an aligning member by sliding and a second side slid in an adaptor groove of the tibial cutting guide, and a handle slidably coupled to the aligning coupler. More particularly, the present invention relates to a coupler assembly for a tibial cutting guide, the assembly enabling an aligner and a cutting guide to be easily coupled and decoupled through an adaptor without specific operation because when the handle is slid to the cutting guide, the handle is fixed to the cutting guide, and the cutting guide and the adaptor are locked, and when the handle is slid in the opposite direction from the cutting guide, the handle is separated from the cutting guide, and the cutting guide and the adaptor are unlocked.