The paper, using the reports of the Security Service of Socialist Republic of Croatia, discusses how the Security Service conducted surveillance of Aleksandar Ranković and his family while they stayed in their holiday house in Dubrovnik, mostly in the summer season. One of the top officials in communist Yugoslavia, Ranković was ousted from power in 1966. Subsequently, the Yugoslav State Security Service initiated “Action X” whose aim was the surveillance of Ranković and his followers. Ranković’s code name in this project was “Petar”. The reports covering the surveillance of Ranković during his stays in Dubrovnik give various data on him, his family, but they also give insight on the techniques used by the Security Service in its secret surveillance of individuals.