Low‐energy ion scattering (LEIS) is introduced as a new analytical technique forinsitumolecular‐beam epitaxy (MBE) monitoring. LEIS is highly sensitive to the atomic structure of topmost layers, and offers an idealinsitumonitoring system. We have built a coaxial impact collision LEIS spectrometer, which is combined with a MBE system. Well‐collimated He+ion beams are provided through the ion beam line and scattered by the substrate surface under MBE growth, and detected by a time‐of‐flight energy analyzer. When the incident direction of the primary beam with respect to the substrate crystal is aligned to a major channeling direction, scattering is limited to the topmost layers, and gives us information on the coverage and epitaxial quality. In order to demonstrate the feasibility of LEIS, we have madeinsituanalysis of MBE growth on InP surfaces. During the layer‐by‐layer growth of InAs/AlAs on As‐stabilized InP(111)A surface, we have observed characteristic variation of the 〈111〉 aligned scattering intensity.