John I (circa 1275–1305) was the Margrave of Montferrat, last the Aleramici dynasty, from 1292 to his death.
John was the only son of William VII of Montferrat and his second wife Beatrice, daughter of Alfonso X of Castile. In his youth, John was put under the tutelage of Thomas I of Saluzzo during the period of William's imprisonment in Alessandria. William died in prison and the peace was upset by Piedmontese rebellions. Charles II of Naples interevened for the defence of John's realm, hoping in the end to install him as his vassal in Piedmont.
With Charles and Thomas, who renewed the investiture of Dogliani, John fought against Alessandria and Asti to recuperate territories lost by his father. He came in conflict with the House of Savoy and Milan. Philip of Savoy possessed Collegno, Grugliasco, Turin, and Pianezza which had been lost by William VII. The league John formed against Matteo Visconti succeeded in chasing him from the city in 1302 and obtaining the submission of Asti in 1303. In January 1305, he fell ill while planning a campaign against Savoy. A few days after dictating his testament, which entrusted his lands to the commune of Pavia, he died and was buried with his forefathers in the abbey of Santa Maria di Lucedio.