A robust guidance law for missile interception was proposed by using the integral sliding mode control (ISMC) scheme. It was shown that the design possesses a remarkable feature that allows the engineer to select in advance an appropriate guidance law for the nominal system according to the interception requirements, so that the state responses of the overall uncertain system will be close to those of the nominal system. It is worth noting that the ISMC scheme forces the system states to be close to those of the RTPN0 at every time instant. Therefore, the effect of the uncertainty by using ISMC does not cumulate, which might explain why the ISMC generally requires smaller maximum control magnitude than that by uncertain or RTPN1. In addition, it is clear that, for a non-maneuvering target, the timing responses by using ISMC will agree with those via nominal or RTPN0.