The synthesis process of large magnesium substituted AlPO -11 single crystals (MgAPO-11) under hydrothermal conditions has been reported. The crystal size and morphology sensitively depend on crystallization conditions and gel compositions. The addition of HF acid in the gel undermines rather than favours the growth of MgAPO-11 single crystals. Using the optimal gel composition with magnesium oxide as the magnesium source, large MgAPO-11 single crystals with good quality have been synthesized in a F free system. The typical crystal dimensions are 25 × 157 ×254 μm , the synthesis temperature is 180°C, and the crystallization period is 60 hours. This journal is © the Partner Organisations 2014.