The aim of this study was to investigate the relationship between the plasma levels of chemokine CCL-2/MCP-1 and acute graft-versus-host disease (aGVHD) and/or idiopathic pneumonia syndrome (IPS) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). ELISA assays were used to detect the plasma level of CCL-2/MCP-1 of 22 patients who received allo-HSCT, including 14 patients without or with grade I, 8 patients with grade II - IV aGVHD, respectively. 8 out of 22 patients were also diagnosed with IPS clinically. The dynamic changes of the plasma levels of CCL-2/MCP-1 chemokine and its correlation with aGVHD and/or IPS were analysized retrospectively. The results showed that the plasma levels of CCL-2/MCP-1 in the patients with moderate and serious aGVHD (grade II - IV) significantly increased, as compared with that prior to allo-HSCT (p < 0.05). The plasma levels of CCL-2/MCP-1 in the patients with aGVHD and/or IPS were higher significantly than those without any of these complications (p = 0.001). The retrospective analysis indicated that the plasma levels of CCL-2/MCP-1 in the patients with IPS significantly increased (p = 0.006). It is concluded that plasma level of CCL-2/MCP-1 correlates with aGVHD and/or IPS, and plays a role in the pathogenesis of these complications.