The oriental tobacco budworm, Helicoverpa assulta, is an oligophagous insect feeding on a few species of Solanaceae plants, including Nicotina tabacum. This study investigated the relationship between H. assulta and plants, focusing on oviposition preference and larval performance of the specialist in host and non-host plants. (1) In choice experiments, N. tabacum and Phaseolus vulgaris were put in a cage with 5 females and 10 males. Most of eggs (ca. 98%) were layed in N. tabacum, whereas few eggs in P. vulgaris. (2) In non-choice experiments, N. tabacum, Datura stramonium, or P. vulgaris was individually put in a cage with 3 females and 6 males, resulting that N. tabacum was the most preferred host, followed by D. stramonium and P. vulgaris. Oviposition was delayed about 2 days in P. vulgaris (a non-host plant) compared to the two host plants. (3) Larval performances were also compared with the three plants. Larval growth was better in N. tabacum followed by D. stramonium and P. vulgaris, High mortality (ca. 100%) of larvae was observed in P. vulgaris, suggesting toxic component(s) derived from the non-host plant might cause the death. The ovipositional avoidance in P. vulgaris is current being investigated to search for the oviposition deterrent, which could be useful for the environment-friendly pest management of H. assulta.