In this study, we performed experiments on the alignment and chaining of non-colloidal, spherical particles suspended in viscoelastic liquid under simple shear flow as a model problem for investigating the microstructure formation in viscoelastic suspensions. Monolayer experiments show that both the chain-like structure and uniformly distributed structure can be observed after the dynamic steady state has been reached depending upon fluid theology. Even though the driving force for the migration is the first normal stress difference of viscoelastic liquid, shear thinning is responsible for the formation of string-like structure. (C) 2003 Elsevier B.V. All rights reserved.