Performance and shape selective effect in the etherification reaction of glycerol to diglycerol by Li-Mg/SBA-15 catalyst was investigated. The reaction was carried out at 240 A degrees C with 2 wt% of catalyst for up to 18 h. The catalyst characteristics were elucidated through surface, SEM and TEM analyses. 10Li10Mg/SBA-15 catalyst showed the highest glycerol conversion and diglycerol selectivity of 77 and 82 %, respectively with corresponding diglycerol yield of 63 %. The distribution of diglycerol isomers was successfully elucidated. alpha beta-diglycerol isomer was predominantly formed in contrast to alpha alpha isomer in homogeneously catalyzed reaction.