This study investigated the presence of sweetness synergism in milk and instant coffee systems. It consists of three parts: 1) modeling concentration-sweetness intensity curves of sweeteners (stevia, sucralose, xylose, tagatose and erythritol); 2) measuring the sweetness potencies of sweeteners compared to sucrose at wide concentration range; and 3) investigating the presence of sweetness synergisms in binary sweetener mixtures. The panelists evaluated sweetness and other sensory characteristics of sweeteners using descriptive analysis. Based on the modeled curve derived from step 1, the concentration of each sweetener with sweetness intensity equal to 2.5% or 2.8% sucrose was calculated for milk and coffee systems, respectively. For the sweetness synergism study, one type of intense sweetener was mixed with one type of bulk sweetener, each eliciting 2.5% or 2.8% equi-sweetness to sucrose, and compared with 5% sucrose added to a milk system or 5.6% sucrose added to a coffee system. The sweetness potencies of bulk sweeteners generally increased whereas the sweetness potencies of intense sweeteners decreased as the concentration increased. The binary sweetener mixtures mostly showed additivity in milk and suppression in coffee system rather than synergism when the concentration dependent nature of sweetness potency for each sweetener was taken into account.