| San Fernando Magnetic Observatory | — | — |
| San Gabriel Observatory | Alicante | — |
| San Pablo-Toledo Magnetic Observatory | — | — |
| San Pere observatory | Mataró | — |
| Sant Celoni observatory | San Celoni | — |
| Sant Gervasi Observatory | Vallvidrera, el Tibidabo i les Planes | — |
| Santa Pola Observatory | Santa Pola | — |
| Segorbe observatory | Segorbe | — |
| Sencelles observatory | Sencelles | — |
| Siena observatory | Ager | — |
| Sierra Contraviesa observatory | Los Vargas | — |
| Sirius observatory | Las Lomas | — |
| Skybor Observatory | Borja | — |
| Slooh.com Canary Islands observatory | Parque Nacional del Teide | — |
| Sobradillo observatory | Sobradillo de Palomares | — |
| SPAG Monfrague observatory | Palazuelo-Empalme | — |
| Telescope Live | Cortijo de las Minas | — |
 Telescopio Jacobus Kapteyn | — | 2.369 m |
| Tenerife Observatory-LCO A, Tenerife | Parque Nacional del Teide | — |
| Tenerife Observatory-LCO B, Tenerife | Parque Nacional del Teide | — |
| Tenerife-LCO Aqawan A #1 | Parque Nacional del Teide | — |
| Tenerife-LCO Aqawan A #2 | Parque Nacional del Teide | — |
| Terminus observatory | Oleiros | — |
| Terrassa observatory | Tarrasa | — |
| Tesla observatory | Valdemorillo | — |
 Tiana observatory | Tiana | — |
| Tocororo Observatory | Arquillinos | — |
| Torreaguila observatory | Barbaño | — |
| Torredembarra observatory | Torredembarra | — |
| Tres Cantos Observatory | Madrid | — |
| TRZ observatory | Caseta de les Mallades | — |
| Tucci Observatory | Martos | — |
| UJA Observatory | Jaén | — |
| Uraniborg Observatory | Écija | — |
| Valldoreix observatory | San Cugat del Vallés | — |
| Valle del Sol Observatory | Torreón de la Tercia | — |
| Vega del Thader observatory | El Palmar | — |
| Ventilla observatory | Madrid | — |
| Via Lactea observatory | Ager | — |
| Vinyols observatory | Viñols y Archs | — |
| Yunquera observatory | Yunquera | — |
| Zaldibia observatory | Zaldivia | — |
| Zonalunar observatory | Valencia | — |
| Zuben observatory | Alhaurín de la Torre | — |