A modified Look-Locker inversion recovery T1 mapping technique was used to study the development of fetal brain. Our study found the MOLLI sequence with a short scan time could reduce the impact of fetal brain movements and perform robust T1 measurements. T1 values differ in brain regions and gestational weeks (from 24 to 36). A negative correlation was found between T1 values and gestational age in thalamus, posterior limb and brain stem. Therefore, T1 measured by the MOLLI sequence could be used as a biomarker for evaluating fetal brain development.