Based on ERA-interim reanalysis daily data during 1979–2019, the impact of Madden-Julian Oscillation (MJO) on Pacific blocking frequency during two types of El Ni?o (Eastern and Central El Ni?o) is examined using a two-dimensional blocking index. Phase 3 and 7 with the higher frequency and the stronger amplitude are selected in this study. It is found that the locations of MJO teleconnections are similar in MJO phase 3 during the Eastern and Central El Ni?o years (EP3 and CP3), corresponding to a positive (negative) geopotential height anomaly in the polar region (the Bering Sea). Thus there are positive blocking frequency anomalies in the high-latitude Pacific sector during the EP3 and CP3. The blocking frequency anomalies over the mid-high-latitudinal Pacific are significantly positive in MJO Phase 7 during the Eastern El Ni?o years (EP7), but are not largely significant in MJO Phase 7 during the Central El Ni?o years (CP7). Because the subtropical westerly jet shifted to the north in the EP7, the MJO teleconnection locates in the north of 50°N. This teleconnection corresponds to the geopotential height anomalies, which increase the Pacific blocking frequency, in the Pacific sector. However, the subtropical westerly jet shifted to the south in the CP7. The teleconnection locates between 40°N and 50°N, resulting in weak influence to geopotential height in the Pacific region. So there are not largely significant blocking frequency anomalies over the Pacific region in the CP7. Finally, the ECHAM4.6 model is used to verify the above conclusions.