The temperature bandwidth of the second harmonic generation (SHG) phase-matching process was investigated for the GdCa4O(BO3)3 (GdCOB) crystal. GdCOB exhibits a much broader temperature bandwidth in comparison with many familiar nonlinear optical (NLO) crystals. For a fundamental wave of 1,064 nm, the maximum temperature bandwidth appeared at (θ=135°, ϕ=47.3°), as predicted by the theoretical calculation and demonstrated by the SHG experiments. The GdCOB crystal is a good candidate for NLO frequency conversions under extreme temperatures.