Piezoelectrics, which can convert mechanical-electrical energy or vice versa, are widely used in sensors, transducers, and actuators. It has been well demonstrated that engineered domains with smaller sizes can contribute to higher piezoelectric performance. However, poling engineered domains with a size less than 1 μm has been a long-standing challenge. Here, we succeeded in creating nanosized engineered domains in two-dimensional (2D) clamped BaTiO₃ ceramics via in situ single-grain poling. The as-obtained domain pattern consists of 90° a–a domains with a width of only ~40 nm, achieving an order of magnitude reduction in domain size compared to the initial state. The creation of nanosized engineered domains mainly results from elastic energy rebalancing under in-plane 2D clamping stresses from surrounding grains, which could be manipulated by poling voltage. Meanwhile, we demonstrate that the nanosized engineered domains exhibit a memory effect during cyclic poling treatments. The present study suggests a promising strategy for engineering nanodomains in piezoelectric materials simply by regulating their dimensions.