The key components of innate immune system such as serum Mannose-Binding Lectin (MBL) levels constitutes principle defense against infections when adaptive immune response is compromised by immunosuppressive drugs. Some studies have shown significant elevation in serum MBL levels in patients with advanced renal failure. The purpose of this study was to see whether elevated MBL levels will decrease after renal transplant (Rtx) and whether MBL deficiency in Rtx recipients increases infectious complications. This study was performed in 71 Rtx recipients and 48 healthy controls. Group (I) were 36 consecutive Rtx recipients whose blood samples were collected for serum MBL levels on a day before Rtx and on days 7 and 14 after Rtx. Patients were followed for 6 months for development of clinically significant infections .Group (II) were 35 stable Rtx recipients from Rtx Clinic who gave consent for this study. Serum MBL concentrations were measured by MBL Oligomer Elisa Kit (www.antibodyshop.com). MBL < 500 ng/ml were classified as low and MBL> 500 ng/ml normal/high. Variables among low and high MBL cases in both groups were compared Results of study in group (I), showed that serum MBL levels is not elevated in advanced renal failure. MBL levels decreased from 1020 in 1 and 2 weeks post Rtx respectively. 1030 and 1562 905 to 16991744 Five of 36 patients who had low serum MBL developed more clinically significant infections (P= 0.008) and more CMV disease (P< 0.0001). In group (II), 10 of 35 patients had low serum MBL levels who had developed more CMV disease since date of Rtx. (P= 0.01). These findings show an important role for serum MBL levels in defense against developing CMV disease after Rtx. It is suggested that low serum MBL levels to be considered a risk factor for CMV disease needing CMV prophylaxis.