Regardless of the slowdown in global warming during the hiatus period, sea surface temperatures (SSTs) in the southwestern Indian Ocean (SWIO) have experienced sustained decadal warming for more than two decades since the mid-1990s. The SWIO SSTs warmed steadily during 1996-2016, causing a warming hot spot of 0.4 K decade-1 in a large region east of Madagascar. An upper-layer heat budget analysis indicated that heat advection by ocean cur-rents was the greatest contributor to the warming of the SWIO SSTs. The existence of an anticyclonic geostrophic current along the western boundary of the SWIO tended to maintain such warming by transporting warmer water from the west into the SWIO region. In addition, net positive heat transport by ocean currents also occurred at the southern boundary of the SWIO as the climatological northward transport of cold water from the Southern Ocean weakened. This reduction in northward ocean currents at the surface was caused by local wind stress changes, lead-ing to a southward Ekman current. Below the surface, an anticyclonic geostrophic current pattern existed around the warming center near the southeastern SWIO, which reduced the transport of cold waters from the Southern Ocean and warmed the SWIO. These processes near the two boundaries formed a self-sustaining positive feedback mechan-ism and favored the maintenance of sustained warming in the SWIO. More attention is needed to analyze the sus-tained long-lasting warming in the SWIO, as it is a unique phenomenon occurring under the background of the ongo-ing global warming.