Microorganisms growing at high salinity and elevated alkaline environments have gained wide attention in term of their unique properties. According to the soluble composition, saline-alkaline environment can be two groups, i.e. "NaCl type" and "soda type (Na₂CO₃/NaHCO₃)". The alkaline pH of the former is relatively low, and that of the latter is higher. This review summarizes validated haloalkaliphilic type strains for optimal growth requiring Na⁺ concentrations above 0.5 mol/L and an alkaline pH of 9, and their biodiversity and physiological characteristics. The biodiversity of the halophilic bacteria is far greater than that of halophilic archaea. Halophilic bacteria are mainly composed of Bacilli (40% of the total), gamma-Proteobacteria (30%), Clostridia (11%), delta-Proteobacteria (6%) and Actinobacteria (6%); Halophilic archaea are Halobacteria (92%) and Methanomicrobia (8%). These extremophiles under double stress play essential roles and functions in biogeochemical processes and the ecological function.