A nanopillar array-based iridium oxide pH sensor was fabricated for a non-invasive tear pH measurement for diagnosing ocular diseases. In this study, a nanopillar structure with a diameter of 600 nm and a height of 1.2 μm was fabricated using soft lithography, and iridium oxide was uniformly coated on the electrode surface via cyclic voltammetry. The as-obtained sensor with a large surface area demonstrated a high sensitivity of -69.14 mV/pH, a fast response time of less than 1 s, and stable sensing performance in a wide pH range of 4~13. Furthermore, a microfluid channel-integrated pH sensor showed high sensitivity and accuracy, effectively detecting pH changes in human samples of tears. The nanopillar array pH sensor, with its high accuracy and repeatability fabricated in this study, can be used to diagnose and analyze ocular diseases.