The green peach aphid, $Myzus$ $persicae$ S$ddot{u}$lzer, is an important sap-sucking pest of many plants, including Chinese cabbage. The objective of the present study was to determine the effects of sublethal concentrations of two insecticides (flonicamid and thiamethoxam) and the action mechanisms on the feeding behavior of $M.$ $persicae$. The median lethal concentrations ($LC_{50}$) of flonicamid and thiamethoxam for adult $M.$ $persicae$ were 2.56 and 4.02 mg/L, respectively. The sublethal concentrations of flonicamid were 0.44 mg/L ($LC_{10}$) and 1.25 mg/L ($LC_{30}$), and those of thiamethoxam were 1.19 mg/L ($LC_{10}$) and 2.45 mg/L ($LC_{30}$). The developmental period of $M.$ $persicae$ nymphs was 5.9 days at $LC_{10}$ and 6.1 days at $LC_{30}$ for both insecticides compared to 5.7 days for the control. Adult longevities at $LC_{10}$ and $LC_{30}$ of flonicamid were 13.2 and 13.7 days, respectively. Adult longevity at $LC_{10}$ of thiamethoxam was 14.7 days. Control adult longevity was 11.6 days. Total fecundity was higher at $LC_{10}$ (41.8 offspring/female) and $LC_{30}$ (43.0 offspring/female) of flonicamid, and at $LC_{10}$ (42.1 offspring/female) of thiamethoxam than that of the control (29.5 offspring/female). Feeding behavior analysis using an electrical penetration graph showed that sublethal doses of flonicamid and thiamethoxam had significant effects on the duration of phloem ingestion. However, higher doses of flonicamid induced starvation by inhibition of phloem ingestion and higher doses of thiamethoxam induced contact toxicity rather than inhibition of feeding behavior. This study provides the basis for a more efficient use of these pesticides in Korea.