Juan de Urtubia[a] (died 1381) was a Navarrese royal squire (escudero del Rey in contemporary documents) who led first a contingent of fifty men-at-arms on an expedition to recover the Kingdom of Albania (1376–1377) and later a large army against Thebes and Boeotia, which he conquered in 1379.
In January and February 1374, Urtubia was rewarded 1,000 Aragonese gold florins, some mills by the bridge at Tudela, and the custody of the great castle of Rocafort by Charles II of Navarre for services rendered.
He led the largest single societas (sub-company) of the company, at fifty men; he appears in the enlistment roll of 15 February 1375 as Johanco durtuvia escudero del Rey ordenado por yr en el dicto biage dalbania e sus eill e en sus governamiento L hombres darmas como parece por un otro mandamiento del Rey.
After the successful conquest of Durazzo with Navarrese help, the Company disappears from view until Urtubia is found in the Morea in April 1378, leading a hundred men or more in the employ of Nerio I Acciajuoli ("Micer Aner" or "Arner").
With the support of Niccolò III dalle Carceri, Duke of the Archipelago on his right and Nerio guarding his rear, Urtubia was secure to besiege Thebes for a long time.