Microband formation in an IF steel during cold rolling at low strain levels (epsilonless than or equal to9.8 %) has been investigated by using TEM. The formation of microbands starts at small reductions (epsilon similar to 6.7 %), and microbands have habit planes running approximately parallel to {110} planes. In the specimen that was rolled to epsilon = 9.8 %, some grains contain one or two sets of microbands, while some are microband-free. The crystallographic measurement and deformation geometry calculation reveal that the habit plane of an observed microband has the largest Schmid factor; and when one <111> slip direction is intensively activated in this plane, one set of microbands is formed on this plane. Two sets of microbands form if two <111> slip directions are strongly and nearly equally activated. In the case of microband-free crystals, up to 7 slip systems have similar Schmid factors, are activated concurrently, and thus produce homogeneous deformation.