One of the distinctive characteristics of the writings of Ambrose of Milan is his frequent and lengthy borrowings from the works of Philo of Alexandria. He treated the 1st-century Jewish philosopher as an authoritative predecessor and made use of his works to a far greater extent than any other Church Father did. This study seeks to fill a lacuna in the current scholarship by investigating Ambrose’s use of Philo in his collection of letters, focusing on a set of three letters concerning the topic of the Genesis creation account (Ep. 29, 31, & 34 [PL#43, 44, & 45]). In all three cases, Ambrose fielded questions on the Six Days of Creation (Hexaemeron) by drawing upon Philo’s treatise De opificio mundi. Each of these letters is undeniably Philonic and yet uniquely Ambrosian. This study seeks to clarify why Ambrose found Philo to be particularly valuable in spite of his Jewishness and also to investigate how Ambrose interpreted, adapted, and ultimately re-created his source.