The ASXL1 gene encodes a chromatin‐binding protein involved in epigenetic regulation in haematopoietic cells. Loss‐of‐function ASXL1 mutations occur in patients with a range of myeloid malignancies and are associated with adverse outcome. We have used lentiviral‐based shRNA technology to investigate the effects of ASXL1 silencing on cell proliferation, apoptosis, myeloid differentiation and global gene expression in human CD34⁺ cells differentiated along the myeloid lineage in vitro. ASXL1‐deficient cells showed a significant decrease in the generation of CD11b⁺ and CD15⁺ cells, implicating impaired granulomonocytic differentiation. Furthermore, colony‐forming assays showed a significant increase in the number of multipotent mixed lineage colony‐forming unit (CFU‐GEMM) colonies and a significant decrease in the numbers of granulocyte‐macrophage CFU (CFU‐GM) and granulocyte CFU (CFU‐G) colonies in ASXL1‐deficient cells. Our data suggests that ASXL1 knockdown perturbs human granulomonocytic differentiation. Gene expression profiling identified many deregulated genes in the ASXL1‐deficient cells differentiated along the granulomonocytic lineage, and pathway analysis showed that the most significantly deregulated pathway was the LXR/RXR activation pathway. ASXL1 may play a key role in recruiting the polycomb repressor complex 2 (PRC2) to specific loci, and we found over‐representation of PRC2 targets among the deregulated genes in ASXL1‐deficient cells. These findings shed light on the functional role of ASXL1 in human myeloid differentiation.