This dataset contains Conductivity-Temperature-Depth (CTD) measurements collected during the research expedition SO303 aboard the RV SONNE. The CTD stations took place in the Indian Ocean from January 14 to February 15, 2024, starting in Port Louis, Mauritius, and operating primarily in the equatorial region. A total of 58 CTD casts were performed across 22 stations.Continuous vertical profiles of physical and biogeochemical water properties were acquired using a Sea-Bird SBE 911plus CTD attached to a rosette water sampler equipped with 24 free-flow bottles (10 L each). The CTD was equipped with flushed dual sensors for temperature (SBE 3), conductivity (SBE 4), and dissolved oxygen (SBE 43). Additional instrumentation included a WET Labs ECO-FLNTURTD sensor for chlorophyll-a fluorescence and turbidity, a Biospherical QCP2350 PAR sensor (paired with a deck SPAR QSR2200 sensor for daylight referencing), and a Benthos PSA-916 altimeter. An Underwater Video Profiler (UVP) was also installed on the CTD frame for all casts.Raw data acquisition and real-time visualization were conducted using Sea-Bird Seasave software (V 7.23.2), with initial conversion and processing routines performed using SBE Data Processing software (V 7.23.2). All temperature, conductivity, and oxygen sensors were calibrated pre-cruise at the DAkkS-certified IOW calibration laboratory. To account for sensor drift and offset, field calibration water samples were collected for salinity and chlorophyll-a analysis; no field calibration was applied to the oxygen probes. This dataset includes the processed, quality-controlled downcast profiles for all 58 casts.