| Siayan | |
| Native Name: | Ditarem |
| Map: | Philippines Batanes#Luzon#Philippines |
| Pushpin Map Caption: | Location in Batanes##Location in Luzon##Location in Philippines |
| Map Relief: | yes |
| Label Position: | bottom |
| Location: | Luzon Strait |
| Coordinates: | 20.9033°N 121.9028°W |
| Country: | Philippines |
| Country Admin Divisions Title: | Region |
| Country Admin Divisions: | Cagayan Valley |
| Country Admin Divisions Title 1: | Province |
| Country Admin Divisions 1: | Batanes |
| Country Admin Divisions Title 2: | Municipality |
| Country Admin Divisions 2: | Itbayat |
Siayan is one of the Batanes Islands, part of an archipelagic province in the Philippines. Also known as Ditarem Island in the native language,[1] the island is about 1/2 mile to 3/4 miles in diameter and lies about north-northeastward of Itbayat Island. The closest island is Mavulis Island which is about north-northeastward of Siayan. There are several detached rocks off Siayan's northeast side, rendering the channel between it and Mabudis unsafe for larger vessels.[2]
Siayan has an elevation of and is listed as an inactive volcano[3] by the Philippine Institute of Volcanology and Seismology.