Mixco Viejo ("Old Mixco"), occasionally spelt Mixcu Viejo, is an archaeological site in the north east of the Chimaltenango department of Guatemala, some 50 kilometres (31 mi) to the north of Guatemala City and 4 kilometres (2.5 mi) from the junction of the rivers Pixcaya and Motagua. It is a moderate sized ruined city of the Postclassic Maya civilization.
The archaeological site and tourist attraction of Mixco Viejo was named after being erroneously associated with the Postclassic Poqomam capital referred to in colonial records by that name. The archaeological site has now been identified as Jilotepeque Viejo, the capital of the Chajoma Kaqchikel kingdom. To distinguish between the two, the ruins of the Chajoma capital are now referred to as Mixco Viejo (Jilotepeque Viejo) while the former Poqomam capital is referred to as Mixco Viejo (Chinautla Viejo).
The ruins are situated at the northeastern extreme of the department of Chimaltenango within the municipality of San Martín Jilotepeque; they are strung out over 1 kilometre (0.62 mi) along a 880-metre (2,890 ft) high ridge approximately 4 kilometres (2.5 mi) from the point where the Pixcaya River flows into the Motagua River, which drains into the Caribbean Sea. The ruins are surrounded by deep ravines dropping off sharply into a tributary of the Pixcaya River. The site is 53.3 kilometres (33.1 mi) from Guatemala City by road.
The site was apparently known to the Chajoma by a variety of names, including Chuapec Kekacajol Nima Abaj (also spelt Chuwa Pek Q'eqak'ajol Nima Ab'aj), meaning "Great stone in front of the Cave of the Children of Night", Zakicajol and Nimcakajpec. Jilotepeque Viejo is estimated to have had a population of approximately 1,500 inhabitants. Jilotepeque was close to the San Martín Jilotepeque obsidian source, giving the inhabitants ready access to the resource.
The site is open to the public and has a small museum. The site was declared a protected archaeological zone by Ministerial Accord 1210 of the Guatemalan Ministerio de Educación ("Ministry of Education") on 12 June 1970.