When microorganisms decompose substances to produce useful materials, that process is called fermentation. Fermentation is used not only for producing foods, but in recent years is also being widely used in industrial fields. In such fields, organic acids, sugars, amino acids, and other groups of compounds are multilaterally measured to understand the fermentation process or optimize conditions. In the case of HPLC analysis, the appropriate separate mode and detection method can differ depending on the component class. This requires multiple independent pieces of equipment for each analysis. This article introduces an example of monitoring a fermentation process using a dual injection system to evaluate two types of analysis simultaneously with only one system.