An analysis of the optical transitions in Er 3+ ions located in Yb 3 Al 5 O 12 (YbAG) crystal is given. The room temperature absorption spectrum from the UV to IR wavelength region have been measured and discussed. The intensity parameters of Er 3+ in investigated host were evaluated using the Judd–Ofelt theory to be Ω 2 =0.27×10 −20 , Ω 4 =0.90×10 −20 , Ω 6 =1.16×10 −20 cm 2 and compared with the values for the YAG:Er 3+ and other erbium doped laser materials. Based on the obtained results the radiative transition probability, branching ratios and radiative lifetimes of the excited states of Er 3+ in YbAG were calculated.