This study proposed a radar rain-rate quality criterion (RRQC), a measure of goodness for the radar rain-rate. The RRQC proposed is based on the similar concept of total variance in the statistical analysis of variance, which considers both the bias and variability of radar rain-rate with respect to the raingauge rain-rate. The RRQC was estimated for three storm events with the raw radar data, along with improved versions based on G/R correction and merging by co-Kriging. Additionally, these radar data were applied to the runoff analysis of the Choongju Dam Basin, Korea. By investigating the relation between the RRQC in the rain-rate input and the errors in the runoff output, a minimum quality of radar rain-rate applicable to the rainfall-runoff analysis was explored.