Background We require a stable model to understand the molecular mechanism by which isolated hyperphosphatemia induces hyperparathyroidism secondary to chronic renal failure.The present study established a rat model of hyperphosphatemia-induced secondary hyperparathyroidism in chronic renal failure.Methods Twenty-nine rats with 5/6 nephrectomy (Nx) were divided into three groups and were fed for 10 weeks on a high phosphate diet (1.2% phosphate) starting from three different post-Nx time points.Parathyroid hormone mRNA in parathyroid gland was measured by real-time PCR and parathyroid cell hyperplasia was tested by proliferating cell nuclear antigen (PCNA) assay.Results The 10 rats fed a high phosphate diet starting from the fourth week post-Nx had isolated hyperphosphatemia and excess synthesis/secretion of parathyroid hormone,and hyperplasia of the parathyroid glands were induced (r=0.86-0.97,P