We investigated the effects of annealing on the crystallinity and mechanical properties of 3D-printed PLA specimens. Specimens with a dog-bone geometry for tensile testing were prepared by fused deposition modeling using a commercial PLA filament. The specimens were annealed at different temperatures in the range 80°C – 120°C fordifferent durations (60 minutes – 24 hours) in dry nitrogen environment. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) characterized the crystallinity and the structure of the specimens. Mechanical properties were determined by tensile testing according to ASTM D638 standard test method. Upon annealing, the disorderedcrystal phase of PLA (α’) transformed into α-phase. Annealing increased the degree of crystallinity in the samples, andhigher annealing temperatures resulted in higher crystallinity. Samples annealed at 80°C for 24 hours showed superiorstrength and higher ductility when compared to as-printed samples. However, annealing at 120°C resulted in reduced ductility, comparable to that of as-printed samples. Samples annealed at 120°C experienced visible warpage due tothermal expansion and structural changes, and the loss of ductility might be attributed to these extrinsic changes. Heat treatments of 3D-printed components is an alternative approach to alter the structure and properties of specimens and provides a new design space for the optimization of 3D-printed parts for various applications.