The desulfurization of the actual heavy crude oil is one of the most important processes in petroleum industries due to the low quality of those types of oil and containing large amounts of sulfur compounds, high viscosity and density. In the present work, the desulfurization of the actual heavy crude oil with a sulfur content 5.8 wt. % from Al-Halfaya Oil Field in southern Iraq was studied using a sodium hydroxideassisted process. Effects of the operating conditions such as: reaction time (30-60 min), temperature (30-50 degrees C), the amount of NaOH in its solution (10-30 gm), and mixing speed (300-500 rpm) were investigated. The desulfurization process was achieved in a batch reactor by implementation of the experimental design technique. The objective function (response) was the sulfur content wt. % while a response surface method (RSM) was applied to define the significant factors that affect the desulfurization process. It was found that effects of the four variables take the following sequence: mixing speed > weight of NaOH > time > temperature. The optimum conditions of the proposed model were obtained using optimization techniques and found as follows: time = 60 min., temperature = 40 degrees C, NaOH solution = 18gm and mixing speed = 500 rpm. The optimum conditions of the sulfur content were applied experimentally and theoretically was equal to 2.5 and 2.3 wt. %, respectively. It is concluded that the efficiency of the sulfur removal content for actual heavy crude oil by this process was 56.89 %. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.