To compare clinical and laboratory features between JAK2 exon12 and JAK2 V617F mutated polycythemia vera (PV) . We collected data from 570 consecutive newly-diagnosed subjects with PV and JAK2 mutation, and compared clinical and laboratory features between patients with JAK2 exon12 and JAK2 V617F mutation. 543 (95.3%) subjects harboured JAK2 V617F mutation (JAK2 V617F cohort) , 24 (4.2%) harboured JAK2 exon12 mutations (JAK2 exon12 cohort) , and 3 (0.5%) harboured JAK2 exon12 and JAK2 V617F mutations. The mutations in JAK2 exon12 including deletion ( =10, 37.0%) , deletion accompanied insertion ( =10, 37.0%) , and missense mutations ( =7, 25.9%) . Comparing with JAK2 V617F cohort, subjects in JAK2 exon12 cohort were younger median age 50 (20-73) years versus 59 (25-91) years, =0.040, had higher RBC counts 8.19 (5.88-10.94) ×10(12)/L versus 7.14 (4.11-10.64) ×10(12)/L, <0.001 and hematocrit 64.1% (53.7-79.0%) versus 59.6% (47.2%-77.1%) , =0.001, but lower WBC counts 8.29 (3.2-18.99) ×10(9)/L versus 12.9