This paper considers the iteration-wise sinusoidal disturbance with a known period but with unknown amplitude and unknown phase in iterative learning control (ILC) applications. An adaptive feedforward compensation (AFC) scheme in the iteration domain is presented to effectively cancel the sinusoidal disturbance. This is an example of using an internal model principle (IMP) in the iteration domain which in fact leads to an ILC updating law with high-order in the iteration direction. A simulation example is presented for illustration.