The morphological features of plants, such as leaf functional traits, are adaptations that enable them to live under different environmental conditions. Thus, leaf functional traits can provide a link between various environmental factors and leaf functions. This study aims to gain insights into the differences in leaf functional traits between healthy (no insect attack) and damaged (serious insect attack) Cerasus yedoensis Yü li. Petiole diameter, leaf length, leaf thickness, ratio of leaf length to petiole length, leaf shape index, and single leaf wet and dry weight of damaged leaves were significantly higher than those of healthy leaves, but lower for leaf moisture and specific leaf area (SLA). Plasticity indices of petiole diameter, petiole length, leaf length, leaf width, and leaf shape index of healthy leaves were higher than those of damaged leaes, but contrary for the plasticity indices of the ratio of leaf length to petiole length, leaf moisture, and SLA of healthy leaves. SLA was positively correlated with leaf moisture but negatively correlated with petiole diameter, leaf length, leaf thickness, ratio of leaf legth to petiole length, leaf shape index, and single leaf wet and dry weight. After serious insect attack, damaged C. yedoensis contained increased quantities of material investment per unit area to exhibit a more efficient anti-herbivore defense; thus, leaf moisture and SLA were decreased, but leaf thickness, and single leaf wet and dry weight were increased. Meanwhile, damaged leaves also were more slender and invested more biomass to the lamina than to the petiole.