San Secondo is a small deserted island located in the Venetian Lagoon, northern Italy.

In 1034 the Baffo family built a church and a convent for Benedictine nuns, with the task to keep a holy image of St. Erasmus.

Starting from 1569, after a fire in the Venetian arsenal, the Republic of Venice moved a powder store here.

In 1824, all the buildings on the island were demolished and it was occupied by a military garrison.

Today the island is completely deserted, and only the small ruins of a redoubt may still be seen.