| Official Name: | Blatná na Ostrove |
| Other Name: | Sárosfa |
| Settlement Type: | Village |
| Pushpin Map: | Slovakia |
| Pushpin Label Position: | none |
| Pushpin Mapsize: | 250 |
| Pushpin Relief: | 1 |
| Pushpin Map Caption: | Location of the village |
| Coordinates: | 48.0069°N 17.4417°W |
| Subdivision Type: | Country |
| Subdivision Type1: | Region |
| Subdivision Name1: | Trnava |
| Subdivision Type2: | District |
| Subdivision Name2: | Dunajská Streda |
| Established Title: | First written mention |
| Established Date: | 1286 |
| Leader Title: | Mayor |
| Leader Name: | Terézia Földváry[1] [2] |
| Area Total Km2: | 10.77[3] |
| Elevation M: | 121[4] |
| Population Footnotes: | [5] |
| Population Total: | 971[6] |
| Population Est: | 879 |
| Pop Est As Of: | 2008 |
| Population Density Km2: | 90.55[7] |
| Demographics Type1: | Ethnicity |
| Demographics1 Title1: | Hungarians |
| Demographics1 Info1: | 87.89% |
| Demographics1 Title2: | Slovaks |
| Demographics1 Info2: | 10.17% |
| Timezone: | EET |
| Utc Offset: | +1 |
| Timezone Dst: | EEST |
| Utc Offset Dst: | +2 |
| Postal Code Type: | Postal Code |
| Postal Code: | 930 32 |
| Area Code: | +421 31 |
| Population Density Sq Mi: | 34.96 |
| Area Total Sq Mi: | 4.16 |
| Elevation Ft: | 397 |
Blatná na Ostrove (Hungarian: Sárosfa, in Hungarian pronounced as /ˈʃaːroʃfɒ/) is a village and municipality in the Dunajská Streda District in the Trnava Region of south-west Slovakia. It has a post-office, a food store, a petrol station, and a bar. There is also a football playground and a public library in the village.
In the 9th century, the territory of Blatná na Ostrove became part of the Kingdom of Hungary. After the Austro-Hungarian army disintegrated in November 1918, Czechoslovak troops occupied the area, later acknowledged internationally by the Treaty of Trianon. Between 1938 and 1945 Blatná na Ostrove once more became part of Miklós Horthy's Hungary through the First Vienna Award. From 1945 until the Velvet Divorce, it was part of Czechoslovakia. Since then it has been part of Slovakia.
The records for genealogical research are available at the state archive "Statny Archiv in Bratislava, Slovakia"