PURPOSE: To determine the minimal optimal functional arterial spin labeling (fASL) sequence duration allowing steady and reproducible motor activation mapping. MATERIALS AND METHODS: Three magnetic resonance imaging (MRI) sessions including fASL and blood oxygenation level-dependent (BOLD) functional MRI (fMRI) sequences were performed on 12 healthy subjects at 3T with a 32-channel coil. The raw 7-minute fASL sequence was truncated to obtain six fASL sequences with durations ranging from 1-6 minutes. All the resulting fASL activations were compared between themselves and with both the 7-minute fASL and BOLD activations. Quantitative parameters assessed activation location (activated volume, barycenter, and distance between barycenters), activation quantification (activation-related cerebral blood flow), and intraindividual reproducibility across fMRI sessions. The statistical analysis was based on analysis of variance (ANOVA) and Tukey's multiple comparisons. RESULTS: Four-minute fASL achieved steady location and quantification of activation with the activated volume corresponding to 81% of the 7-minute fASL volume and a barycenter located 1.2 mm from the 7-minute fASL barycenter and 3.0 mm from the BOLD fMRI barycenter. Four-minute fASL reproducibility was high and statistically equivalent to 7-minute values. CONCLUSION: A 4-minute fASL sequence is thus a reliable tool for motor activation mapping and suitable for use in clinical practice.