The moth Lymantria xylina Swinhoe (1903) (Lepidoptera: Lymantriidae) is a major defoliator of hardwood and fruit trees in Taiwan. Although the plants identified as host plants of L. xylina usually refer to plants used as food or as shelter, most of the host plant identifications have not considered the role of these hosts on larval development. This study investigated various instars feeding on different plants to assess the developmental diet breath of L. xylina. Forty-seven plant species, belonging to 25 families were used in feeding trials. Various bioassays, including first instar survival and long-term feeding trials, indicated the most suitable host plants for the different developmental stages. Results of the first instar survival trial indicated that first instars could survive only on 13 of the tested plant species. In addition, first instars could only successfully grow to pupa on seven of these 13 test plants species. To assess the developmental diet breath shifts of this moth, 38 plant species (excluding those nine plant species that the first instars did not feed upon) were fed to third and fifth instars in long-term feeding trials. Survival to pupa was noted on 12 and 13 test plant species for the third and fifth instars, respectively. In short, we found that the larvae performed differently when fed on various host plants and that the host plant range increased with the larval stage. Therefore, it is necessary to adjust the host plant range of this moth and to consider host plant breadth together with the developmental stages of caterpillars.