The focus of this research was to implement a new RP-HPLC-PDA method for determining cannabidiol (CBD), which has been established with the help of Quality by Design (QbD). Design expert (version 12) software was used to conduct the factor screening studies. The mobile phase ratio, flow rate, and temperature conditions were used as independent variables, while retention time, peak area, and peak tailing were used as dependent variables in a Box-Behnken design. The best separation was obtained with acetonitrile and water as mobile phase in the ratio of 45:55 % (v/v), a flow rate of 1.0 ml/min, and an oven temperature of 30 °C with PDA detection at 210 nm. The newly optimized method showed the concentration linearity range in µg/ml (1187.57 - 5997.83) of CBD with an excellent correlation coefficient R2 = 0.9951. The % recovery of the CBD was obtained between 97.84 to 99.34 %, and the % RSD was not more than 2 %, thus clearly confirming the high level of accuracy for analysis. The technique was assessed under the ICH guidelines, which revealed excellent linearity, precision, and robustness. Consequently, the approach was used to determine the retention time of the drug in its nanoemulsion formulation, which revealed no substantial change in retention time.