Single-cell pH-sensing and accurate detection and label-free fast identification of cancer-cells are two long-standing pursuits in cell and life science, as intracellular pH plays a crucial role in many cellular events and fates, while the latter is vital for early cancer theranostics. Numerous methods based on functionalized nanoparticles and fluorescence probes have been developed for cell pH-sensing, but are often hindered for single-cell studies by their main drawbacks of complicated probe preparation and labeling, low sensitivity and poor reproducibility. Here we report a simple and reliable method for single-cell pH imaging and sensing by innovative combined use of UV-Vis microspectroscopy and common pH indicators. Accurate and sensitive pH detection on single-cell or sub-cell level with good reproducibility is achieved by the method, which enables facile single-cell pH profiling and label-free rapid identification of cancer-cells (due to distinguishable intracellular pH levels) for early cancer diagnosis, and may open a new avenue for pH-related single-cell studies.