Agia Aikaterini, Orthodox church building in Plaka, Greece.

Agia Aikaterini is an 11th-century Byzantine church on Agia Aikaterini Square in Plaka, built as a four-column cross-in-square with an Athenian-type dome. Its east side has three apses, the central one with a three-light window; the walls mix brick with cloisonné-like detailing over rough stone. A 19th-century portico wraps the north, west and south sides, and the dome was rebuilt taller between 1917 and 1927.

Built in the second quarter of the 11th century, the church was first dedicated to Saints Theodore. Abandoned later, it was given in 1767 to the Sinai Monastery of Saint Catherine and repaired by the Sinaite monk Ionas, who rededicated it to Saint Catherine. Damaged around the 1821 revolution, it was restored by 1850 with funds from parishioners, and the monastery was sold to the Athens archdiocese in 1889.

The church was originally dedicated to Saints Theodore, and an inscription on the altar column records this. In 1767 it became a metochion of Saint Catherine's Monastery on Sinai, whose monks rededicated it to Saint Catherine and planted the palm trees in the courtyard. The future Ecumenical Patriarch Athenagoras served here as a deacon.

The church stands on Agia Aikaterini Square beside the Monument of Lysicrates, with two Roman-era columns at the square's edge. The palm trees in the forecourt were planted by the Sinai monks; Roman bath ruins also survive in the courtyard. The building is an active parish church, so visits fit around services.

The church was first dedicated to Saints Theodore Stratelates and Theodore Tiro; the dedication inscription survives on the column that serves as the altar's base. The marble altar rests on a fragment of an ancient column, and two mismatched capitals on the eastern columns, carved with reed leaves, were reused from the early Christian period.