Cellular microstructure formation and the incorporated stress distribution in a binary alloy system are simulated using a phase field model. Elastic stress and strain induced by volumetric contraction due to solidification is considered. Tensile stress is, as a whole, observed in the solidified region, while a complicated stress distribution is generated at the interfacial area. The solid-liquid interface shows a wavy pattern with the tips and bottom edges under the conditions considered, while remarkably large stress is generated below the tips. Under a certain condition, the microstructure becomes complex inducing cell coalescence, liquid droplets, and grooves between cells. Stress concentration and the characteristic distribution are then generated around a droplet. Stress dependency on the phase transformation is also introduced in the formula, and simulations are carried out to show its effect on the pattern formation. Provided the transformation is accelerated under tensile stress, solidification advances faster at the bottom than at the tip, until eventually a flat interface is observed at the growing front. (C) 2009 Elsevier BM. All rights reserved.