The mechanical properties of polymers change over time when they are exposed to UV light and moisture. This work presents the results of continuously exposing a nylon-based composite used in additive manufacturing (AM) to UV light and humidity for 24-, 48-, 96-, 168-, 336- and 504-hour periods. Sample coupons were printed in a Markforged Two ® composite printer using Onyx ®, which is a nylon matrix composite reinforced with short carbon fibers. For UV exposure, the samples were exposed to commercial 253 nm UV lamps, whereas for humidity, an ACE UV-260 humidity chamber was used at 50% relative humidity and 22°C with bi-distilled water. The effects of said variables were measured using the Charpy impact energy (per ASTM D6110), water absorption, and Shore hardness D (per ‎ASTM D2240). It was found that nylon indeed presents 1.03% ±0.28 water absorption over as little as 24 hr of exposure and about 5.6% ±0.48 water absorption for 504 hrs. Regarding the Charpy impact energy, the absorbed energy decreases from 450 kJ/m^2 ±15.96 at 24 hr to 254 kJ/m^2 ±33.9 at 504 hr of humidity exposure. The Shore hardness D varies from 59.1±0.82 for zero exposure to 59.7 ±1.5 at 24 hr and 66.8±2.5 after 504 hr of UV exposure. We can conclude that water absorption makes nylon a more fragile material, whereas UV exposure hardens the material. Future results could include using tensile axial tests and infrared spectroscopy to assess water absorption.