Heating tests of pure diolein with various chloride and glycidyl ester (GE) levels at 240°C were conducted. Tetrabutylammonium chloride (TBAC) was used as a chloride source. The GE levels tended to converge on equilibrium around 100 mg-as monochloropropane-1,2-diol (MCPD)/kg, regardless of the initial GE content, which suggested that the GE level was the result of competitive reactions between generation and decomposition. Chloride content had no influence on GE generation. On the other hand, 3-MCPD ester levels were greatly influenced by both chloride and initial GE content, and the reactions were estimated to reach completion in the early stage of the heating period due to the run-out of the chloride source. The conversion ratios of chloride to 3-MCPD ester were 2–8%. These low ratios indicated that most of the TBAC was converted to inactive compounds for 3-MCPD ester formation. Not only the quantity but also the type of chloride compound is important to control the 3-MCPD ester level. Although generation of 3-MCPD esters via GE was confirmed, practical impact was estimated to be small. However, this pathway should be taken into consideration, because GE is thought to make 3-MCPD monoester, which could show different bioavailability compared with the diester that predominantly occurs in edible oils.