A clamping device of a flexible rod for a minimally invasive surgery contains a retaining set and a flexible rod. The retaining set includes a locking member and a clamping seat. The locking member has an inner hexagonal hole defined therein and outer threads formed on an outer rim thereof. The clamping seat has a concaved arcuate face defined on a bottom end thereof and axially connecting with the locking member. The flexible rod is circular and is retained with the concaved arcuate face of the clamping seat.