Deli Serdang (Indonesian: Kabupaten Deli Serdang; Jawi: دلي سردڠ) is a regency in the Indonesian province of North Sumatra. It surrounds the city of Medan, and also borders to the west the city of Binjai, which is effectively a bedroom community for Medan. The entire regency lies within the Medan metropolitan area. It occupies an area of 2,497.72 km² (964.38 sq miles). The capital of the district is Lubuk Pakam, which is located approximately 30 km east of Medan. The national census of 2000 recorded 1,573,987 people, but by 2010 the regency's population increased by 13.76% to 1,790,431,^[2] and at the 2020 Census the total was 1,931,441.^[3] The official estimate as at mid 2023 was 2,018,164 (comprising 1,014,629 males and 1,003,535 females).^[1] Kualanamu International Airport is located in this regency.

It is the most populous regency in Indonesia outside the island of Java. Its population is comparable to the country of Latvia.

The external boundaries of the regency are with:

• To the north: the Langkat Regency and the Strait of Malacca.
• To the south: the Karo Regency and Simalungun Regency.
• To the east: the Serdang Bedagai Regency and the Strait of Malacca.
• To the west: the Karo Regency, Langkat Regency and the city of Binjai.

The city of Medan is an enclave within the regency.

The regency is divided into twenty-two districts (kecamatan), tabulated below with their areas (in km²) and their 2010 Census^[2] and 2020 Census^[3] populations, and the official estimates as of mid 2023.^[1] The table also includes the locations of the district administrative centres, the number of administrative villages within each district (totaling 380 rural desa, and 14 urban kelurahan), and its post code:

Notes: (a) Deli Tua, Deli Tua Barat and Deli Tua Timur. (b) Kenangan and Kenangan Baru. (c) Galang Kota. (d) Pekan Tanjung Morawa.
(e) Cemara, Lubuk Pakam I, II Lubuk Pakam Pekan, Lubuk Pakam III, Paluh Kemiri, Petapahan and Syahmad.

Deli Serdang Regency contains three plantations owned by London Sumatra (LONSUM).^[4]

On 21 June 2003, farmers and indigenous peoples in a number of villages within the district attempted to re-occupy lands which had been leased to LONSUM by the government.^[5] Police fired upon the group, resulting in at least a dozen wounded and four deaths.^[5]

• Sultanate of Deli
• Sultanate of Serdang