AMR is the major complication of renal transplantation that significantly affects the allograft survival. Complement fixation of Donor specific anti-HLA antibodies is the hallmark of AMR. Different methods have been developed to detect harmful DSAs. However, not all DSAs have the same detrimental effect, as different antibody characteristics (timing, specificity, strength, and complement-fixing ability) might trigger distinct immune responses. Here, we assessed DSA characteristics in renal transplant patients. Thirty-nine patients with de novo DSA were analyzed for the DSA MFI values, C1q positivity and IgG subclasses. IgG1 was the predominant IgG subclass (49.4%), followed by IgG3 (24.7%), IgG2 (16%), and IgG4 (9.9%). Among DSA characteristics, DSA MFI and IgG1 subclass were strongly correlated with C1q positivity (p= 0.01 and p= 0.009, respectively). Further studies are needed to investigate the clinical relevance of high MFI DSA and IgG1 subclass in improving the utility of the C1q assay in predicting graft outcomes.