The transparent and homogeneous ErCa 4O(BO 3) 3 (ECOB) crystal is grown by Czochralski method. The room temperature absorption spectra have been measured and compared with that of 0.1 mol ErCl 3 solution. According to Judd-Ofelt theory, the spectral strength parameters: Ω 2=1.673×10 -20 cm 2, Ω 4=1.356×10 -20 cm 2, Ω 6=0.156×10 -20 cm 2 of Er 3+ ion have been fitted. The radiative transition probabilities A J,J′, oscillator strengths f J,J′, radiative lifetime τ and the branching ratio β J′ have been calculated. From these parameters, the properties and applications were discussed.