In the earlier work done by the author for the reactor pressure vessel (RPV) material 20MnMoNi55 steel, Monte Carlo simulation technique is shown as an effective statistical technique to calibrate Weibull modulus “m” and Weibull scale parameter “σu” for temperatures −100 °C, −110 °C, −120 °C, −130 °C, and −140 °C by performing only six fracture toughness tests instead of (30 × 5 = 150) number of tests. But it lacks validation with the experimental work. So, in this paper, huge numbers of fracture toughness tests (minimum 30 for each temperature) are performed experimentally at −100 °C, −110 °C, and −130 °C in the lower self of the ductile-to-brittle transition (DBT) region for the RPV material 20MnMoNi55 steel. Then, linear regression analysis of the experimental data is performed to calibrate Weibull modulus m and Weibull scale parameter σu of Beremin (a cleavage fracture model) for the above mentioned temperatures. The calibrate values show a matching trend with that of experimental calibrated values and justify the prediction capability of Monte Carlo simulation to predict the Beremin model parameters with the help of only six fracture toughness tests. This statistical simulation procedure can be considered as an effective technique for the proper calibration of Beremin model parameters for any material.