A series of layered double hydroxide (LDH) were synthesized by the coprecipitation method under different physical and chemical conditions. The composition and structure of LDH were determined and characterized by chemical analysis, XRD and IR, and the effects of such factors as equilibrated pH, initial ratio of mixed Mg/Al solution, reaction temperature and drying temperature upon crystallinity, Mg/Al ratio, structure and Mg and Al hydrolysis percentage of synthesized LDH were also investigated. The results indicate that the best conditions for synthesising LDH in this experiment seem to be initial Mg/Al 2:1,pH 10 and synthesis temperature 50℃. Under these conditions, solid products are characterized by single LDH phase, Mg/Al ratio of LDH 2∶1, high crystallinity, Mg hydrolysis percentage 99.21% and Al hydrolysis percentage 98.97%.