The effect of enzymatic interesterification of a margarine formulation containing fish oil was studied by comparing the physical characteristics of the interesterified products with the same formulation without any modification process. Based on a response surface formulation design, thirteen oil blends containing palm stearin (PS) (60 to 90%), palm kernel oil (PKO) (10 to 40%) and fish oil (FO) (0 to 10%) were interesterified by Lipozyme TL IM (Thermomyces lanuginosa) using a continuous packed bed reactor (PBR). FO in the blend had a similar effect as PKO on solid fat content (SFC) but a stronger influence than PKO was observed in the interesterified product. Interesterified products contained higher solid fat at a temperature range from 5 to 30 C than the blend. Enzymatic interesterification has an advantage compared to blending since the former led to products having a sharp melting point, which enabled a reduction in SFC at body temperature. This thesis also looked into a possibility of applying a dual lipase system for interesterification of lipids. Enzymatic interesterification of palm stearin/ CnO oil blend (70/30 w/w %) was conducted by applying a mixed lipase system. Enzyme mixtures containing two types of lipases, both immobilized or combination of immobilized with non-immobilized lipase, were prepared to study their effect on the interesterification of the oil blend in batch and continuous reactors. Combination of Novozym 435 with Lipozyme TL IM and RM IM, mixture of immobilized enzymes, led to an improvement of the enzymatic activity in a batch reactor. An improvement was also observed in reaction by lipase AK Amano 20 mixed with Lipozyme TL IM, a combination of non-immobilized with immobilized lipases. The co-immobilization action from the carrier of the immobilized lipase towards the free lipase was proposed to be one of the reasons leading to synergistic effect. No apparent synergistic effect was observed in the combination of Lipozyme TL IM and RM IM when applied to a continuous reaction. Enzyme inactivation can be affected by polar compounds, trace elements of metals, primary and secondary oxidation products. In conducting enzymatic interesterification of oils and fats, it is important to use a good quality substrate in order to achieve the highest enzyme stability. Refined oil is preferred than crude oil since most of the compounds which caused the enzyme inactivation have been removed. Freshly refined oil contains neither oxidation products nor free fatty acid. However the oxidation products and FFA would increase over a period of time, depending on the storage condition, which could aggravate the enzyme stability. A pre-column was installed in a continuous PBR for enzymatic interesterification of sunflower oil and fish oil blend. The pre-column functions as a protector of the enzyme bed to prolong the lifespan of the enzyme. Deactivation kinetic of enzymes subjected to interesterification using a pre-column was compared against without a pre-column. The deactivation rate of enzyme bed without a pre-column was 7.4 times faster than the one with a pre-column, where the half-life were 8 and 58 days respectively.