Central to the production of adaptive behavior is the ability to learn the temporal order of behavioral elements (e.g., A, B, C). Yet little is known about neural substrates of serial order in self-initiated behavioral sequences. The present study assessed the contributions of specific dorsal striatal regions to the acquisition of serial order in mice, using a two-action sequence task without instructive cues. Excitotoxic lesions of the sensorimotor (dorsolateral) striatum dramatically impaired the acquisition of a simple sequence; in contrast, lesions of the associative (dorsomedial) striatum had no significant effect. Neither lesion caused gross motor impairments or affected the learning of nonsequential actions. These results demonstrate for the first time a critical role of the sensorimotor striatum in the learning of serial order.