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Stricter environmental regulations and trend of decreasing cost and increasing operational efficiency are the driving forces for the improvement of the tribological performance in many different industries. For example, in the case of hydropower plants, there has been increasing research carried out to achieve oil-free stations, which would substitute the oil-based lubricants with environmentally accepted lubricants or water. In this application, water could be a good alternative due to its availability and low cost. Also, water is non-toxic and has high heat capacity. Although advantageous, using water as a lubricant presents many challenges that limit its application such as corrosiveness and thin lubricant film due to its physical properties. Therefore, the material selection for the interacting surfaces needs to be correctly performed when considering water-lubricated conditions because of the harsher tribological conditions to which they will be susceptible. Polymeric materials, such as Ultra High Molecular Weight Polyethylene (UHMWPE), are good candidates for such water-lubricated applications due to versatile mechanical and thermal properties, as well as good tribological characteristics. Today, these materials find use in different tribological components, such as, bearings, liners, and gears. However, high wear rates limit their applications, due to the reduced operating life. The performance can be improved in different ways, including surface modification, polymer blending, and use of reinforcements. A novel research area is hybrid and multiscale reinforced composites, which combines the use of micro and nanofillers to obtain improved performances. UHMWPE has been thoroughly studied, including mechanical, thermal and tribological behavior. However, there are limited studies on the effects of hygrothermal aging on the friction and wear response of UHMWPE. The studies are even more restricted when considering reinforced materials. Therefore, this work aims to investigate the effect of hygrothermal aging in the tribological performance of UHMWPE composites in water-lubricated conditions. Aging exposure and tribological tests were performed to evaluate the response of the materials, and the main conclusion of this work is that the tribological response of UHMWPE composites was not significantly affected by the test exposure conditions.