In this article, we describe an ultrahigh vacuum (UHV) compatible superconducting quantum interference device (SQUID) magnetometer system for investigations of surface, interface, and thin film magnetism. This system provides a new capability for a commercial SQUID magnetometer to characterize freshly deposited thin film samples transported from a separate molecular‐beam epitaxy deposition facility without breaking vacuum. Magnetic measurements can be performed over a wide range of temperatures down to 4.2 K in applied magnetic fields as high as 1 T, and under a variable vacuum environment in which pressures as low as 10−10Torr can be achieved. The combination of the extremely high sensitivity of the SQUID for magnetic measurements with UHV analysis techniques offers the unique capability for films to be prepared, processed, and characterized repeatedly without substantial contamination. The capabilities of the UHV‐SQUID magnetometer system are demonstrated byinsitumeasurements of the magnetic properties of Co/CoO bilayered thin films grown on Si(100) single‐crystal substrates by electron‐beam evaporation. ©1995 American Institute of Physics.