In the face of global climate change it is estimated that the frequency and intensity of high temperature events during summer will increase in the future. The understanding of how affected aphid and aphid-symbiont relationships and how to increase tolerance in the ongoing global warming is a critical issue. Aphids are major agricultural pests thus it is important to evaluate the effects of high temperature stress from the viewpoint of pest management. The objectives of this study were to investigate the effects of high temperature stress on the growth and reproduction of aphids and obligate intracellular endosymbiont Buchnera, has a critical effect on aphid survival and reproduction. We evaluated the effects of heat shock on the pea aphid, Acyrthosiphon pisum Harris (Hemiptera: Aphididae), and its obligate endosymbiont Buchnera aphidicola by means of quantitative PCR in the treated aphids and their offspring after heat shock to analyze how high temperature stress affects the growth of both Buchnera and aphids. First-instar aphids received a single heat shock (35°C for 6 h), repetitive heat shocks (repeat of the single heat shock for 3 days), and control (a constant 20°C). Heat shock negatively affected aphid body length and Buchnera and EF1α densities. Heat-shocked aphids contained lower densities of Buchnera and EF1α than did control aphids when body length was kept constant. Heat-shocked aphids contained lower Buchnera densities relative to EF1α densities. Some heat-shocked aphids became sterile as their Buchnera density was lower than a threshold. The offspring of aphids subjected to a single heat shock recovered the amount of Buchnera, but repetitive heat shocks treated aphid exhibited markedly lower Buchnera and EF1α densities. Thus, heat shock negatively affects both aphid and Buchnera cell proliferation, this could reduce aphid growth, development, reproduction and possibly leads to extinction of local populations.