Experimental investigations have been conducted to elucidate the variation of the dynamic interfacial tension (DIFT) in the process of alkaline flooding for heavy oil. The Binnan heavy oil with high TAN (Total Acid Number) and the Zhuangxi heavy oil with low TAN were pre-equilibrated by long-term contacting with NaOH and Na2CO3 solutions. The results show that the heavy oil pre-equilibrated by NaOH solutions almost loses the interfacial activity, and the IFT increases a lot. Although there is still interfacial activity in the heavy oil which is pre-equilibrated by Na2CO3 solutions, and the dynamic interfacial tension minimum (DIFTmin) changes a little, yet the dynamic interfacial tension equilibrium value (DIFTeq) increases a lot. The effect of interfacial reaction on the interfacial property of oil with low TAN is more severe than that with high TAN. When the alkaline concentration is larger than a certain value, the IFT between the fresh oil with high TAN and the equilibrated alkaline solutions can decrease to ultralow after interfacial reaction, and the Na2CO3 system is superior to the NaOH system. However, the IFT between the fresh oil with low TAN and the equilibrated alkaline solutions increases after interfacial reaction. The above results can be used as guidance in the formulation design and mechanisms studies of alkaline flooding for improved heavy oil recovery. (C) 2012 Elsevier Ltd. All rights reserved.