[Objectives]  To investigate intra and interspecific attack and defensive behaviors of the fall armyworm, Spodoptera frugiperda (J. E. Smith) and the corn earworm, Helicoverpa armigera (Hübner), important maize pests that engage in cannibalistic behavior and compete for food and habitat, and thereby further understanding of interspecific relationships between these species in the field. [Methods]  Under indoor food conditions, 15 instar combinations of 4-6 instar larvae of S. frugiperda and 4-6 instar larvae of H. armigera were set up, the frequency of competitive behavior was observed, and the types and times of attack and defense behaviors of S. frugiperda and H. armigera were recorded within 20 min. [Results]  Attack behavior was the predominant form of intraspecific competition in H. armigera, and was more obvious in competition between 5th and 6th instar larvae. The frequency of head touching in 5th instar larvae, and the frequency of strike behavior in 6th instar larvae, were the highest, accounting for 46.1% ± 3.1 % and 51.0% ± 2.3%, respectively, of all competitive behaviors. Both species displayed attack behavior during interspecific competition. The frequency of strike behavior was significantly higher, and recoil behavior significantly lower, in 4th instar S. frugiperda larvae than in 4th instar H. armigera larvae. The frequency of head touching was significantly higher, and the frequency of recoil and retreat behavior significantly lower, in H. armigera during competition between 5th instar S. frugiperda and 5th instar H. armigera larvae. There were no significant differences in the frequencies of competitive behaviors between 6th instar S. frugiperda and H. armigera larvae. The frequency of head touching was significantly higher in 6th instar larvae than in 5th instar larvae, but the frequency of recoil and retreat behavior was significantly lower, both for S. frugiperda and H. armigera. Fourth to 6th instar larvae of S. frugiperda had similar survival rates (83.3%, 86.6% and 80.0%, respectively) in competition with the same instar of H. armigera (76.7%, 73.3% and 63.3%, respectively). Survival of 5th instar S. frugiperda and H. armigera larvae was 80% and 56.7%, respectively, which is significantly lower than the survival of 6th instar larvae, which was 100% for both species. [Conclusion]  Interspecific competition between S. frugiperda and H. armigera can be intense. S. frugiperda had no obvious competitive advantage in competition with H. armigera larvae of the same instar, but 6th instar S. frugiperda larvae were competitively superior to 5th instar H. armigera larvae.