Rapid, sensitive, selective, convenient, and cost‐effective pathogen diagnosis is important to prevent further spread of pandemic diseases, minimize social and economic losses, and to facilitate right clinical therapy. Over the past few years, various sensor‐based diagnostic systems outperforming conventional pathogenic diagnostic assays have been developed. Among them, colorimetric biosensors detecting target molecules by the naked eye have attracted much attention due to their simplicity, practicality, and cost‐effectiveness. Recently, nanomaterials have been adopted as a versatile signal transduction and amplification tool for rapid and sensitive detection of pathogenic bacteria and viruses. Here, recent trends and advances are reviewed in detecting and diagnosing pathogenic bacteria and viruses using colorimetric biosensors employing various nanomaterials. In addition, it is discussed how nanomaterials and bioreceptors can be better integrated together to develop rapid and sensitive colorimetric detection system in the future.