The calculated distance (air line) between Zemun and Sremska Mitrovica is approximately 40 miles respectively 64 kilometers.
By car or train, the actual journey to Sremska Mitrovica is certainly longer, as only the direct route (as the crow flies) between Zemun and Sremska Mitrovica has been calculated here.
Air line (approximately)
64 kilometers
34 nautical miles