In a recent paper, “ferroelasticity” has been defined on the analogy of “Ferroelectricity,” mechanical strain and stress in the former corresponding to electric polarization and field in the latter. Just as “antiferroelectricity” is associated with “ferroelectricity.” so is “antiferroelasticity” associated with “ferroelasticity.” It is considered that antiferroelastic crystals are possible. For the purpose of grasping them conceptually and knowing their characteristics and also for the purpose of understanding more deeply ferroelectricity and antiferroelectricity, this paper presents and thermodynamically investigates some model crystals which are antiferroelastic as well as paraelectric, ferroelectric, or antiferroelectric. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.