Abstract： Objective To provide a reliable differential diagnosis among the progressive supranuclear palsy ( PSP), striatonigral degeneration ( SND ) and Parkinson disease ( PD ) . Methods Conventional MRI data in clinically proved PSP(8 cases), SND(9 cases), PI)( 12 cases)and 12 normal controls were retrospectively analyzed. Midbrain area, pons area, ports diameter and middle eerebellar peduncles width were measured. The ratio of pons area over midbrain area (pons area/midbrain area) was calculated in all patients and normal controls. Then one way ANOVA and a Kruskal-Wallis H test were used for statistical analysis. Results Midbrain area of the PSP group [ (85. 8±12. 0) mm2 ] was the smallest, and there was statistically significant difference ( P < 0. 05 ) comparing with the SND group [ ( 133.2± 8. 4) nun2 ], PD group[ ( 133. 5±10. 8) mm2 ] and the control group [ ( 135.9±7.5 ) mm2 ]. There was no overlapping in the distribution of midbrain area between the PSP group(66.0-98. 2 mm2 ) and SND, PD and normal groups( 116. 2-142. 1, 110. 8-146. 2 and 121.7-145.8 mm2 ). The pons area-midbrain area ratio (P/M) of the PSP group (5.9±0. 8) was the largest in four groups, and there was statistically significant difference ( P < 0. 05 ) comparing with the SN D group ( 2. 9±0. 5 ), PD group ( 3.8±0. 3 ) and the control group (3. 8±0. 3 ). There was no overlapping in the distribution of P/M between the PSP group(5.0-7.2) and SND,PD and normal groups(2. 2-3.5, 3. 3-4. 6 and 3. 2-4. 2). SND group had the smallest P/M, pens area, pons diameter and middle cerebellar peduncles width [ 2.9±0. 5, ( 384. 8±62. 6) mm2 , ( 18. 6±2. 0) nun and( 12. 9±2. 4) mm ] in all groups, and significant difference ( P < 0. 05 ) was found comparing with the PSP group[5.9±0. 8, (500.1±21.8)mm2, (22. 7±1.7)mm and( 16. 3±1. 1) nun],PD group[3.8±0.3, (500.2±25.8)mm2, (23.7±1.0)mm and(16.8±1. 1)mm]and the control group [3. 8±0. 3, ( 508. 8±20. 6 ) mm2, ( 23.2±1.2) nun and ( 16. 4±0. 9 ) mm]. But the PD group and control group had no statistically significant difference in the midbrain area, pans area, pons diameter, P/M and middle cerebellar peduncles width ( P > 0. 05 ). Conclusion MRI measurements helps in the differential diagnosis among PSP, SND and PD.