Stradivari’s apprenticeship is still not completely understood today. Tradition has it that he was a pupil of Nicola Amati, the great violin maker who preceded him in musical instruments production in the city of Cremona. However, no documents proving Stradivari’s presence in Nicola Amati’s workshop can be found. In this paper, we present a dendrochronological analysis of Stradivari’s harp, the only surviving portable diatonic harp, now in the possession of the Museum of the Conservatorio San Pietro a Majella, Naples. The harp bears the inscription “Ant:◦ Stradivarivs Cremonen.s F. 1681” engraved on the column. Dendrochronological analysis of the soundboard revealed high correlation values (TBP > 16) between the tree ring sequence of the harp and that from a Nicola Amati cello made in 1679, suggesting that the wood of the two soundboards comes from the same tree trunk. The dendrochronological analysis of the harp offers new evidence of Stradivari’s possible apprenticeship and has stimulated reflection on the wood trade for making musical instruments during the golden age of Italian classical violin making (16th–18th centuries).