Objective To explore the diagnosis value of morphology changes of pleomorphic megakaryocytes in the bone marrow (BM) smears and BM sections in chronic MPD(CML-CP, ET,PV and PMF). Methods BM aspiration was taken in 182 patients of MPD aspiration and biopsy examination was performed synchronously to obtain the BM smears and BM sections samples. The BM smears were subjected to Wright/Giemsa stain and immunohistochemistry stain, while the BM sections were subjected to Haematoxylin-Giemsa-Fuchsin stain. The morphology of pleomorphic megakaryocytes was classified into five groups, which were Ⅰ type ( inclusion type), Ⅱtype ( hypolobulated muclei type), Ⅲ type ( giant hyperlobulated nuclei type), IV type (micro pyknotic type), and V type(extrusion type). The size of megakaryocytes clusters was recorded as no clusters(0) , predominantly small clusters of fewer than 6 cells (1) or predominantly large clusters of at least 6 cells (2) . The detection rates of various types of pleomorphic megakaryocytes and megakaryocytes clusters were both analyzed in the BM smears and BM sections. Results In CML-CP group, the detection rates were (3. 73±3. 84)% , (14.19 ±7. 62)% ,(5.99 ±4.67)%, (34. 37 ±10.79)%, (9.45 ±6. 87)%, (32. 28 ±7. 67)% and 3.13 ±2. 30)% ,(12.61 ± 9.28)%,(4.94±4.27)%,(35.26±9.63)%,(9.47 ±5.89)%,(34.58 ±6.81)% for I tⅠype,Ⅱ type,Ⅲ type, Ⅳtype and Ⅴ type pleomorphic megakaryocyte in BM smears and BM sections. There were no significantly differences between the BM smears and BM sections(t value were 0.524,0.510,0.645, 0.239,0.011,0. 869,all P>0.05). In ET group, the detection rate of I type [ (6.17 ±2. 89)% ] in BM smears was significantly higher than that in BM sections [ 2.42 ± 1. 28) % ] (t = 7. 183, P < 0. 01) , while the detection rate of V type [ (6. 28 ± 3. 34) % ] in BM smears was significantly lower than that in BM sections [ (10. 18± 4.03) % ] (t = 3.940, P < 0.01). Besides these, the detection rates of other types were not significantly different between the BM smears and BM sections(t value were 0.079,0. 122,1.643, 1. 638,all P>0. 05). In PV group, the detection rate of V type in BM smears [ (6. 55 ±4. 11)% ] was significantly lower than that in BM sections [ (10. 30±3. 34) % ] (t = 2. 351, P < 0.05 ). However, the detection rates of the other types were not significantly different between the BM smears and BM sections (t value were 1. 635,0. 301,0. 132,0. 704,0. 681 ,all P' >0. 05). In PMF group, the detection rate of IV type in BM smears [(13.05 ±5.24)%] was significantly lower than that in BM sections [(29.14± 8. 72) % ] (t = 5. 245, P < 0. 01). And the detection rate of normal type in BM smears [ ( 33. 58 ± 14.39)% ] was significantly higher than that in BM sections [(23. 01±7.96)%] (t =2. 132,P<0. 05). Besides these, the detection rates of the other types were not significantly different between BM smears and BM sections( t value were 0. 787,0.646,2.062,0. 869, P > 0. 05 ) . In CML-CP and PV groups, the detection rates of size of clusters were not significantly different between the BM smears and BM sections (x~2 = 2. 772, P > 0. 05 ). In ET group, the detection rate of small clusters (1) in BM smears was obviously higher than that in BM sections, however, the detection rate of larger clusters (2) in BM smears was obviously lower than that in BM sections (x~2 = 13. 748, P < 0.01). In PMF group, the detection rate of no clusters(0) in BM smears was obviously higher than that in BM sections, however, the detection rate of large clusters(2) in BM smears was obviously lowers than that in BM sections (x~2 =18.741 ,P<0. 01). Conclusions Both BM smears and BM sections can be applied to observe pleomorphic megakaryocytes. The morphology changes of pleomorphic megakaryocytes have certain reference values for identification of MPD subtypes and differential diagnosis.