Abstract: Objective To establish a radioimmunoassay（RIA） method for measurement of calcitonin gene-related peptide（CGRP） in rats. Methods A radioimmunoassay（RIA） method was established using recombinant rat CGRP-thyroglobulin（TG） and 125I-CGRP in New Zealand rabbits to obtain high titer anti serum.Plasma CGRP levels in rats and mice with cerebral ischemia/reperfusion（I/R） injury and controls were measured. Results The standard curve covered 0.1-24.3ng/ml.The intra-and inter-CVs were 2.5% and 6.6%,respectively.The sensitivity was 0.1ng/ml and the recovery rate was 104%-107%.The plasma CGRP levels were significantly higher in rats and mice with cerebral I/R injury than in controls（P＜0.01） and well correlated with their normal ranges（P＜0.05）. Conclusion The RIA method for measuring CGRP in rats we established can be used in measurement of CGRP levels in models of cardio-cerebral diseases.