Clutch size variation of a leaf mining moth Paraleucoptera sinuella Reutti was investigated on two host plants, Populus sieboldii Miquel and Salix miyabeana Seemen. We found that female moths oviposited egg clutches with different size on the two host plants and that clutch size was correlated with leaf area between host species. Therefore, we concluded that females are adjusting clutch size in response to variation in resource availability for offspring. Positive correlation was also found between clutch size and leaf area within host species, however, the relationship was weak. Expected clutch size was determined from estimates of leaf area consumed by a larva until pupation. Females laid significantly smaller clutches than the expected size that could be supported by a single leaf on both host plants. We discussed how the females determined clutch 2size in response to resource availability.