Purpose: To compare between accuracy of optical and ultrasonic biometry in IOL calculation in high myopic cataractous patients to achieve the desired postoperative refraction. Methods: Pro-spective, Comparative, Randomized Interventional study included 50 eyes with axial length of 26.5 mm or more divided into 2 groups: Group (1): (optical biometry group) included 25 eyes and Group (2): (ultrasonic biometry group) included 25 eyes. Haigis formula was used for intraocular lens power calculation. Phacoemulsification with intrabagal IOL was performed. The 2 groups were compared preoperatively for axial length (AL), K readings and Ant chamber depth (ACD) and they were compared postoperatively for spherical equivalent (SE), prediction error (PE) and mean absolute error (MAE) one month postoperatively. Results: the study was conducted on 50 eyes who were divided into 2 groups. As regard preoperative measures, mean AL measured by optical biometry was 28.76±1.56 mm whereas that measured by ultrasonic biometry was 28.58±1.55 mm with a mean difference of 0.18±0.27 mm, which was statistically significant (P <0.05) whereas other parameters: k readings, ACD, were nearly comparable in both groups. (P > 0.05). As regard the postoperative results, the difference between 2 groups in postoperative spherical error, prediction error and mean absolute error was also not statistically significant (P > 0.05), however better postoperative refractive outcomes were noticed with optical biometry. Conclusion: optical biometry provides more accurate measurements of biometric parameters, especially axial length than applanation ultrasonic biometric in high myopic patients, also Haigis formula is preferred with high myopia, providing acceptable postoperative refractive outcomes with both methods.