Abstract: Objective In order to establish the animal model for research on the damage of melamine to urinary system, the effects of melamine at different dosages to rats were investigated .Method Sixty days old SPF SD rats were divided into 4 groups，one group was set as a blank control and fed with 10 g/L solution of methyl cellulose every day, the other 3 groups were treated with melamine at a level of 0.25, 0.5, 1.0 g/kg，respectively. All groups were administered continuously for 6 weeks. After 6 weeks， the kidney, ureter and bladder of anatomized rats from all groups were observed with both naked eye and stereo-microscope to determine their shape changes, and then the organ coefficients were calculated.Meanwhile, blood biochemical parameters of rats were measured and their kidneys were scanned by small live animals Micro-CT to evaluate the morphological changes. Results After 6 weeks’treatment of melamine, the average vesical and renal calculus formation rate was 66.6% (20/30) and 56.6% (17/30)，respectively. The kidneys from each experimental group were all bigger than that form control group and with distinguished greyish yellow color. There were yellow, cord-shaped sediments which integrate into flakes or granules in the kidneys, and arc-shaped yellow halo was formed between the cortex and medulla. Renal mass, organ indices and CREA, BUN, phosphorus and magnesium content in serum of rats from each treatment group were also significantly higher than that from control group (P＜0.01). Conclusion Part of the SD rats were induced with different degrees of urinary stones after 6 weeks’treatment with melamine at the level of 0.5～1.0 g/kg. Based on these data，the animal model for research on the damage of melamine to the urinary system was established.

Key words: Melamine, Urinary calculus, Disease model, Rat