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In this work, the influence of the thermomechanical degradation of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) during melt processing on the formation of its crystalline structure was investigated by temperatureresolved small angle X-ray scattering (SAXS) and complementary techniques, thus combining different tools in the characterization of polymeric structures. PHBV was processed in an internal mixer at 170 C for 7 minutes at four rotation speeds (50, 100, 150, and 200 rpm), in order to obtain samples with molar masses ranging from 125 000 to 64 000 g mol −1. The processing at higher rotation speeds resulted in the formation of thinner, smaller, and/or imperfect crystallites, which melt at lower temperatures. Moreover, the melting curves were broader than those associated with the unprocessed PHBV, suggesting a change in the size distribution of the crystallites. These results were corroborated by lamellar long period values and crystalline and amorphous thickness as determined by SAXS, where the sample processed at 200 rpm presented the most evident effects of the melt processing. K E Y W O R D S crystallization, processing, SAXS, thermal properties 1 | INTRODUCTION Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) is a biodegradable and biocompatible random copolymer of natural origin with a great interest as a substitute for conventional thermoplastics in several applications, including packing industry, drug delivery, tissue engineering, among others. [1] However, PHBV is sensitive to high temperatures and shear stresses associated with melt processing. [2] Both of these factors cause a drastic