The subcritical crack growth resistance in water of a Y-Si-Al-O and Y-Si-Al-O-N glasses has been investigated with three point bending experiments. It has been shown that the SCG behaviour of the Y-Si-Al-O-N glass is superior to that of the Y-Si-Al-O glass. This is reflected by the power law exponent n which is 21 for the Y-Si-Al-O glass and 63 for the Y-Si-Al-O-N glass. Mechanistic implications of these observations are discussed.