Objective To explore the impact of high glucose on the expression of ubiquitin mRNA and ubiquitinated-protein in cultured rat glomerular mesangial cells(GMCs). Methods Cultured HBZY-1 rat GMCs were divided into 5 groups: normal glucose group (5.6 mmol/L), high glucose group(10, 20, 30 mmol/L). Mannitol group was used as high osmosis control. The expression of ubiquitinated-protein and ubiquitin mRNA of each group was measured by Western blot and real-time PCR respectively. Results Ubiquitinated-protein was mostly macromolecule. Compared with normal glucose group, the expression of ubiquitinated-protein was increased significantly in a dose- and time-dependent manner in 20,30 mmol/L glucose groups (all P＜0.01), and the expression of ubiquitin mRNA was also increased obviously (P＜0.05). Conclusions High glucose can obviously increase the expression of ubiquitinated-protein and ubiquitin mRNA, and upregulate ubiquitin-proteasome pathway in cultured GMCs