Thanks to near-surface sea temperatures measured at Trieste, northern Adriatic Sea, from 1899 to 2015, we estimated mean daily temperatures at 2 m depth and built a quasi-homogeneous 117-year-long time series. We describe the instruments used and the sites of measurements, which are all within Trieste harbour. The data set represents a valuable tool to study sea temperature variability on different timescales. A mean temperature rise rate of 1.1 ± 0.3 °C per century was estimated.