Acerola by-products (AB) have been used as raw material for extracting active compounds; however, there were no studies related to the use of the remaining acerola by-product (RAB) from this extraction. This portion still has fibers and can be used for the production of cellulose nanofibrils (CNFs); therefore, the main objective of this study was to evaluate the production of CNFs using AB and RAB and to investigate whether the extraction can be a treatment step before bleaching/acid hydrolysis. AB and RAB were characterized before and after being chemically treated (AB_CT and RAB_CT, respectively). The fibers extracted from the RAB showed the highest cellulose contents (RAB: 36.6 % and RAB_CT: 69.9 %), suggesting that the extraction process had an impact on by-product defibrillation. The same trends were observed for CNFs produced by acid hydrolysis. CNFs based on RAB showed higher yield (CNF_RAB: 25.2 % and CNF_RAB_CT: 24.2 %), higher crystallinity index (CNF_RAB: 68.3 % and CNF_RAB_CT: 71.7 %) and higher thermal stability compared to CNFs extracted from AB and AB_CT. This study proved that it is feasible to use by-products after removing the active compounds for CNF production without other pre-treatments or in association with chemical treatment to obtain more crystalline and thermally stable CNFs.