High amino acid content in tempeh and lactose in whey powder can be combined to perform Maillard reaction. So, it can be used to produce functional food products. This is caused by the formation of Amadori and melanoidin as water-soluble compounds which are reported to have high antioxidant capacity and produce a preferred flavor. The general objective of the study was to obtain an optimum process condition in a mixture of water soluble tempeh extract and whey powder with the highest antioxidant capacity (100 mL). The research method was carried out in three  stages, namely (i) optimation condition of the Maillard reaction between water soluble tempeh extract and whey powder (concentration of whey powder and pH reaction) (ii) optimation of temperature and time for reaction, and also study kinetics of Maillard reactions that occur based on changes in antioxidant capacity, (iii) analysis an optimal mixture of water soluble tempeh extract and whey powder that has undergone a Maillard reaction. The analysis of  the antioxidant activity was carried out using DPPH method, browning intensity, and color analysis using chromameter. The results of the analysis of antioxidant activity showed that the mixture ratio of  water-soluble tempeh extract with whey powder 5 % b/v (100 mL), reacted at 100 °C and pH 5 for 90 minutes can increase the antioxidant activity of the mixture from  67,91 ± 2,62 % to 89,89 ± 0,17 %. That concludes as the optimum condition for Maillard reaction between water-soluble tempeh extract and whey powder.