Optical quality Nd:GdCa4O(BO3)3 (Nd:GdCOB) crystal and chromium sensitized crystal of Cr:Nd:GdCa4O(BO3)3 (Cr:Nd:GdCOB) were grown by the Czochralski (CZ) method. The transmittance spectra was measured at room temperature on 7at%Nd:GdCOB and 1at%Cr:7at%Nd:GdCOB samples. The absorption in the blue-UV region of Cr:Nd:GdCOB was larger than that of Nd:GdCOB, which matched the xenon flash lamp very well. A 3×3×10 mm3 Nd:GdCOB sample without any antireflective coating was side-pumped using a pulsed dye-laser tuned to 595.4 nm. The green-light output energy was 1.35 mJ at a pump energy of 17.5 mJ. The conversion efficiency was 7.7%, and the threshold energy was less than 1.2 mJ which are the best results up to now to our knowledge. 3×3×7 mm3 Nd:GdCOB and Cr:Nd:GdCOB samples without antireflective coatings were pumped using a flash pump source. The threshold for Cr:Nd:GdCOB was 0.9 J while for Nd:GdCOB it was 1.0 J. The output green light energy was 2.46 mJ for Cr:Nd:GdCOB at a 10 J flash pump energy and was 1.96 mJ for Nd:GdCOB at the same pump energy, which clearly shows that Cr3+ ions have the sensitizing effect on the Nd3+ ions in Nd:GdCOB crystal.