Abstract： Objective To study the developmental process of the region of basal nuclei of postmortem fetuses by 3.0 T and 7.0 T MRI.Methods One hundred and thirty-one postmortem fetuses of 14 to 40 weeks of gestational age(GA)were scanned by 3.0 T MR,of which 11 fetuses of 14-27 weeks of GA were chosen and scanned by 7.0 T MR. The time when the structures in the region of basal nuclei could be detected and the changes of MR signal intensity were analyzed for MRI of different Tesla.Results On 3.0 T MRI.the dorsal thalamus could be delineated as early as 14 weeks of GA. The germinal matrix, caudate nucleus,and putamen could be visualized as early as 15 weeks of GA. The globus pallidus could be described as early as 18 weeks of GA.and the internal capsule and external capsule could be shown as early as 20 weeks of GA. The signal of the caudate nucleus during 15-30 weeks of GA was relatively hypointense on T1WI and hyperintense on T2WI.but during 31-40 weeks of GA, it was relatively hyperintense on T1WI and hypointense on T2WI. The putamen had a relatively high signal intensity on T1WI and low signal intemity on T1WI during 15-17 weeks of GA, and it appeared patchy during 18-25 weeks of GA,then it had a relatively low signal intensity on T1WI and high signal intensity on T2WI during 26-30 weeks of GA, and during 31-40 weeks of GA,its signal intensity was relatively high on T1WI and low on T2WI.The globus pallidus had a relatively high signal intensity on T1WI and low signal intensity on T2WI during 20-40 weeks of GA Compared to the 3.0 T MRI,the T2 images of 7.0 T MRl were more clear,and most structures in the region of basal nuclei could be clearly displayed as early as 16 weeks of GA.such as the germinal matrix,caudate nucleus,dorsal thalamus,putamen,globus pallidus,internal capsule,and external capsule.The claustrum could be delineated as early as 18 weeks of GA on 7.0 T MRI. Conclusions 3.0 T MRI could show the developmental process of the region of basal nuclei well,but the T2 images of 7.0 TMRl were comparatively better.