Based on the emission structure of (TCTA/TCTA(0.5)TPBi(0.5)/TPBi) doped with 10% (pq)(2)Ir(acac) [hereafter, (TCTA/TCTA(0.5)TPBi(0.5)/TPBi):(pq)(2)Ir(acac)], new red phosphorescent organic light emitting diodes with different host structures in thickness were fabricated and evaluated. Among the devices with various thicknesses of TCTA in a range of 50 angstrom similar to 150 angstrom in the limits of 100 angstrom-thick TCTA(0.5)TPBi(0.5) and 300 angstrom-thick total host, the best electroluminescent characteristics was obtained in the device with emission structure of [TCTA (80 angstrom)/TCTA(0.5)TPBi(0.5) (100 angstrom)/TPBi (120 angstrom)]:(pq)(2)Ir(acac). In this device, current density, luminance, and current efficiency were found to be 98 mA/cm(2), 15,800 cd/m(2), and 16 cd/A at an applied voltage of 9 V, respectively. The maximum current efficiency was 24.5 cd/A under a luminance of 50 cd/m(2). The peak wavelength in the electroluminescence spectral distribution was 606 nm. The color coordinates were (0.62, 0.37) on the CIE (Commission Internationale de I'Eclairage) chart.