Field-evolved resistance to Cry1F maize in Spodoptera frugiperda (J.E. Smith) populations in Brazil was reported in 2014. In this study, to investigate fitness costs, we constructed a near-isogenic S. frugiperda- resistant strain (R-Cry1F) using Cry1F-resistant and Cry1F-susceptible strains sharing a close genetic background. A near-isogenic R-Cry1F strain was obtained by eight repeated backcrossings, each followed by sib-mating and selection among resistant and susceptible strains. Fitness cost parameters were evaluated by comparing the biological performance of resistant, susceptible, and heterozygous strains on artificial diet. Fitness parameters monitored included development time and survival rates of egg, larval, pupal, and egg-to-adult periods; sex ratio; adult longevity; timing of preoviposition, oviposition, and postoviposition; fecundity; and fertility. A fertility life table was also calculated. The near-isogenic R-Cry1F strain showed lower survival rate of eggs (32%), when compared with Sus and reciprocal crosses (41 and 55%, respectively). The number of R-Cry1F insects that completed the life cycle was reduced to ∼25%, compared with the Sus strain with ∼32% reaching the adult stage. The mean generation time (T) of R-Cry1F strain was ∼2 d shorter than R-Cry1F♂ × Sus♀ and Sus strains. The reproductive parameters of R-Cry1F strain were similar to the Sus strain. However, fewer females were produced by R-Cry1F strain than R-Cry1F♀ × Sus♂ and more females than R-Cry1F♂ × Sus♀. In summary, no relevant fitness costs are observed in a near-isogenic Cry1F-resistant strain of S. frugiperda, indicating stability of resistance to Cry1F protein in Brazilian populations of this species in the absence of selection pressure.