The optical properties of a transparent optical resin (HMA/ST) containing ternary rare earth complex are reported. Based on Judd-Ofelt (J-O) theory, the J-O parameters were calculated to be omega2 = 10.139 4 x 10(-20) cm2, omega4 = 3.810 9 x 10(-20) cm2, omega6 = 9.050 7 x 10(-20) cm2 by using the emission spectrum of optical resin containing Eu (TTA)3 phen-0.31 wt%. The J-O parameters were used to calculate the total radiative transition rate (456.6 s(-1)) and radiative lifetime (2 190.1 micros) of the excited state 5D0. The stimulated emission cross-sections a and the fluorescence branch ratio beta parameters for the transitions of 5D0 --> 7F(J), (where J' = 1, 2, 4 and 6) were also evaluated. By analyzing the calculated J-O parameters, it is concluded that the excited state of Eu3+ in optical resin has a long radiative lifetime and large emission cross-section, which shows that the optical resin containing rare earth complex can be used for stimulated emission amplification or as a laser material.