For the preparation of well-defined H₂O-soluble C₆₀ polymers, several C₆₀-PEG conjugates were prepared from a C₆₀ biscarboxylic acid derivative and monodisperse NH₂-PEGs (NH₂-EG_n, n = 4 - 36) via amide conjugation. When the relatively long PEGs (EG_n, n ≥ 12) were employed, the C₆₀-PEG conjugates became completely H₂O-soluble by forming micelle-like structure shown by the data of surface tension, DLS, and cryo-TEM. Interestingly, these H₂O-soluble C₆₀-PEG conjugates (C₆₀(EG_n)₂, n = 12 - 36) showed reversible thermoresponse to form larger aggregates (ca. 1 μm by DLS) at higher temperatures. The temperature for the aggregation was related to the lengths of PEGs attached to C₆₀; 29 °C (C₆₀(EG_n)₂, n = 12), 51 °C (n = 20), and 72 °C (n = 36). This thermoresponse was speculated to occur by dehydration of well-organized PEG chains in the micelle-type structure of monodisperse C₆₀-PEG caused by gauche-to-anti conformational change of PEG anchors. This thermoresponse of well-defined amphiphilic C₆₀-PEG conjugates indicates potential applications in areas such as temperature sensors and thermoresponsive materials.