The protein abundance of the UT-A1 urea transporter in kidney inner medulla (IM) is dramatically increased under diabetic conditions, particularly the highly glycosylated 117 kDa form of UT-A1. This change is consistent with the increase in urea permeability in the perfused rat inner medullary collecting duct (IMCD). In diabetes the diacylglycerol (DAG) – protein kinase C (PKC) pathway is activated. It is not known whether and how the elevated DAG and activated PKC pathway contribute to the increased kidney IMCD urea permeability under diabetes conditions. In this study, diabetic animal model was induced in SD rats by tail vein injection of streptozotocin (62.5 mg/kg BW). At 14 day, kidney IM was dissected and cell plasma membrane was isolated by sucrose gradient ultracentrifugation and used for lectin pullown. Diabetes causes significant UT-A1 glycan changes of increased sialic acid as demonstrated by sambucus nigra lectin (SNA) pulldown assay. We then investigated the role of PKC in UT-A1 protein expression. Treatment of 2 μM PDBu, the protein kinase C (PKC) activator, significantly increases UT-A1 protein abundance in UT-A1 MDCK cells. The glycan structure change of UT-A1 was examined using sugar-specific binding lectins. Interestingly, activation of PKC markedly increases UT-A1 glycan sialic acid. Rat kidney IMCD suspensions were prepared and treated with 2 μM PDBu for 4 h. Activation of PKC by PDBu specifically increased UT-A1 sialylation from kidney IMCD. Functionally, increased UT-A1 sialylation has enhanced urea transport activity when the UT-A1 MDCK cells were incubated with 2 mM sialic acid for 24 h. Our study suggests that activation of DAG- PKC pathway may participate in elevated tubular urea reabsorption by increasing UT-A1 sialylation, which plays an important role to prevent the osmotic diuresis caused by glucosuria under diabetic conditions.