Irradiation of melon (Cucumis melo) seedlings with red LED light (wavelengths of 620 to 630 nm) at an intensity of 1×10¹⁸ photons m^－2 s^－1 decreased the number of Thrips palmi (melon thrips), a major insect pest that causes serious damage during greenhouse melon cultivation. Thrip populations were significantly lower than in treatments without LED, both with continuous 24-h irradiation and with 12-h daytime (06:00 to 18:00) irradiation. Transplanted seedlings were also irradiated with red LED light of two different intensities (4.7×10¹⁸ photons m^－2 s^－1 or 1.0×10¹⁸ photons m^－2 s^－1) in two cultivation environments (glass or plastic greenhouse). These findings suggest that irradiation with red LEDs may be an effective means of controlling Thrips palmi in greenhouse melon cultivation.