Existing numerical models of mixing processes in oscillatory baffled reactors (OBR) are mainly Eulerian-based. An alternative Lagrangian based methodology, Smoothed-Particle Hydrodynamics (SPH), for predicting flow patterns and assessing mixing performance is presented in this paper. A bespoke SPH solver is developed for single phase modeling, as it is, for the first time, applied to OBR, and the results are compared with those from Eulerian modeling, i.e. Finite Volume (FV) method. SPH has successfully captured the expected flow characteristics in OBR as clearly and equally as its Eulerian counterpart, validating the SPH method. Since SPH provides historical information of individually tracked fluid packets/particles in the domain of interest, it allows for readily quantitative assessments of mixing without additional models. Two new indexes to assess mixing and plug flow efficiency have been proposed by making full use of SPH's capabilities.