The calculated distance (air line) between Knjazevac and Sremska Mitrovica is approximately 163 miles respectively 263 kilometers.
By car or train, the actual journey to Sremska Mitrovica is certainly longer, as only the direct route (as the crow flies) between Knjazevac and Sremska Mitrovica has been calculated here.
Air line (approximately)
263 kilometers
142 nautical miles