Glasses with cation composition of M: Si: Al = 3.45:3:2 (where M = Er and Y) with varying nitrogen contents (0, 5, 8, 15 and 22 eq.%) have been prepared by ball milling in alcohol media. These Er-and Y-sialon glasses were heat-treated at temperatures in the range of 950-1200 degrees C for 10 h to study the crystal phase(s) obtained. Samples were characterised by SEM and XRD and obtained data from XRD were further analysed to obtain unit cell parameters of some phases. It is shown that it is possible to obtain B-phase (Y2SiAlO5N) from these glass compositions with relatively low nitrogen contents (5 and 8 eq.% N) but with different unit cell parameters (i. e. a = 3.77-3.81 angstrom and c = 9.83-9.97 angstrom) to those reported previously in the literature, suggesting that there are some compositional differences between B-phases obtained from different nitrogen content glasses as well as different modifier cations. Long-term heat treatment studies revealed that the stability range of temperature for Er-B-phase is more extensive than its Y-B-phase equivalent.