Little Aya Sofya (Turkish: Küçük Ayasofya Camii) is a historical mosque in Istanbul, Turkey. It is located in the Eminönü neighbourhood of the city, on the European side of the Bosphorus Strait, and is known for its beautiful architectural features and rich history. 

The mosque is also known by its original name, the Church of the Saints Sergius and Bacchus, as it was initially built as a Byzantine church in the 5th century AD.

Little Aya Sofya is a small but elegant building with a central dome and four smaller domes. The mosque's exterior is adorned with intricate carvings and decorations, including calligraphy, geometric patterns, and glazed tiles. 

The mosque's interior is equally impressive, with a large central prayer hall and a series of smaller prayer rooms. The walls and ceiling of the mosque are adorned with beautiful frescoes and calligraphy.

Little Aya Sofya is an active place of worship and is open to the public. It is an important site for the city's Muslim population and is a popular destination for tourists and pilgrims. The mosque is a beautiful and historic site and is a must-see destination for anyone interested in the history and culture of Istanbul.