Through the partial substitution of Y3+ ions with La3+ ions in the structural framework of YCa4O(BO3)3, the Yb3+-doped mixed oxyborate Y1−xLaxCa4O(BO3)3 (x = 0.09 and 0.25) crystals have been grown and characterized. The La3+ content (x = 0.25) in the crystal far exceeds the La3+ doping limit (x = 0.1) previously reported, whereas the crystal remains transparent and free from cracks. Optical absorption, emission and fluorescence decay measurements have been performed at room temperature, and the influence of La3+ doping on the spectroscopic characteristics of the crystals has been presented and discussed in detail. The main spectral and laser parameters pertinent to laser potential have been evaluated and compared with those of other oxyborates. The perspectives for application of the Yb3+:Y1−xLaxCa4O(BO3)3 crystals as laser media have been discussed.