The commune is located in the south-central part of the county, on the border with Călărași County. It lies on the right bank of the Ialomița River, just south of the county seat, Slobozia, and 127 km (79 mi) east of Bucharest.
Ciulnița is crossed by county road DJ201, which connects it to the west to Albești, Axintele, and Coșereni (where it ends in national road DN2) and to the east to Slobozia, Mărculești, and Țăndărei (where it ends in DN2A [ro]). The Ciulnița train station serves the CFRMain Line 800, which connects Bucharest with the Black Sea coast.
