The evaluation of oil well cement additives is determined by the influence on the rheological and mechanical properties of the slurry. The use of nanoadditives for cement, such as bacterial nanocellulose (BNC), has been increasing in recent years due to their high tensile strength, high Young ’s modulus, and thermal resistance. However, the influence of BNC addition on the mechanical properties of the cement is not widely studied. The purpose of this work is to understandthe effects caused by the addition of BNC in class G cementduring the fresh and hardened states. Free fluid and high-pressure consistometry tests have been carried out in the fresh state. In the hardened state, dynamic thermomechanical analyses (DMA) and uniaxial compressive strength (UCS) tests have been performed. Additionally, thermogravimetric analysis (TGA) was carried out to determine the calcium hydroxide content and the hydration degree (DOH). Results indicate that BNC modifies the slurry behavior by reducing the free fluid content and by incrementing consistency. Moreover, the calcium hydroxide content and DOH increase with the addition of BNC. The mechanical properties of BNC-cement samples are increased in terms of storage modulus and mechanical strength. These properties can improve the performance of cement used in cementing operations.