Existence of water in crude oil results in a number of problems such as equipment corrosion and reduces value of oil. Therefore, one major necessary process after extracting oil should be water separation. In this regard, different methods are commonly used. One of the most common methods is application of chemical demulsifiers. Concerning the aforesaid, various researches have been done toward development. One of the methods used for optimizing operation of chemical demulsifiers deals with adding nanoparticles. In this thesis, the effect of nanoparticles of aluminum oxide, titanium oxide and magnesium oxide in different weight percentages for three chemical demulsifiers related to one of the Iranian oil regions were investigated. The results of bottle test shows performance improvements via using demulsifiers for two types of crude oil, whereas, the third oil type experienced a dramatic decrease in performance of demulsifier sample. Based on conducted experimental results, adding 0.06% (weight fraction) of Magnesium Oxide nanoparticle to suitable demulsifier for light oil gives the highest separation and improved demulsifier performance by 30%, while, efficient concentration for suitable demulsifier for Forouzan oil determined in 0.08% weight concentration of Titanium Oxide nanoparticle and improved demulsifier performance by 16%. Adding nanoparticle to the suitable demulsifier for heavy oil had a negetive impact in all nanoparticle concentrations.