Abstract： Objective To estimate the value of diffusion tensor imaging (DTI) in early diagnosis of chronic allograft nephropathy (CAN) and monitoring of graft fibrosis in rat models . Methods Thirty CAN rat models were established as experimental group by transplanting Fisher donor kidneys into Lewis recipients. Thirty Lewis rats that received Lewis kidneys served as control group. Serum creatinine (SCr) was monitored regularly every two weeks from 14 days after transplantation. Eight rats were randomly selected by random number table method and underwent DTI examination at 4, 12, 20 weeks after modeling. DTI scans were performed on the renal cortex and medulla to measure apparent diffusion coefficient (ADC) and fractional anisotropy (FA). From the remaining 22 rats in each group, 6 rats were randomly selected and underwent pathological analysis at 4, 12, 20 weeks after modeling. Histological changes in the kidney were evaluated by chronic allograft damage index (CADI) scores. The expression of alpha-smooth muscle actin (α-SMA) and Vimentin were quantitatively measured. The differences in creatinine, DTI parameters, CADI score, α-SMA, Vimentin expression level were analyzed by two independent samples t test in two groups, the differences among CADI score, α-SMA, Vimentin expression level of the experimental group were compared using ANOVA. The correlations among DTI parameters and CADI score, α-SMA and Vimentin expression level were analyzed using Pearson analysis. Results The creatinine in the experimental group increased continuously, and the creatinine in the control group showed no significant increase. The difference in creatinine between the two groups was statistically significant from 8th week after operation (P＜0.01). There was no obvious difference in the size and signal intensity of transplanted kidneys in control group at different time points. Compared with the control group, the graft kidney in the experimental group at the 4 weeks demonstrated increased signal intensity with mild increased volume of kidney, and the boundaries between cortex and medulla were not clear. The cortex and medulla showed gradually increased signal intensity, heterogeneous signal distribution and marginal haziness over time. The ADC and FA value of renal cortex and medulla in experimental group were significantly lower than those in control group at 4, 12, 20 weeks (P＜0.05). The ADC and FA values of the cortex and medulla gradually decreased in the experimental group over time, while the values of the parameters in the control group did not show a significant decrease. The ADC and FA values of the cortex and medulla were negatively correlated with the scores of CADI, and the expression level of α-SMA, Vimentin in the experimental group(r=－0.50 to －0.85, P＜0.01).Conclusion DTI can be an effective technique for early diagnosis of CAN and monitoring of graft fibrosis process.