Poly(lactic acid) (PLA) is biodegradable thermoplastic polyester produced from renewable sources that can be easily processed to yield articles to be used in either the industrial packaging field. The large influence of the crystalline structure and morphology on biodegradation rate, as well as on the other material properties, led to an ever-increasing interest in the study of the crystallization kinetics of PLA along the years. Several investigations on the crystallization kinetic of PLA under quiescent condition were carried out. However, the description of the evolution of morphology under shear conditions is still challenging and even the basic principles of the phenomenon are not well understood yet, because of the experimental difficulties of obtaining direct measurements of nucleation and growth rates during flow. In this work, experiments of nucleation density and growth rate of spherulites were carried out and under continuous shear at different temperatures and shear rates. Furthermore, in order to investigate the nucleation and growth rate at higher shear rates, step shear tests were conducted by applying the shear flow when the crystalline structures have already reached dimensions easily detectable by an optical microscope. On analyzing the evolution of radial growth rate during the steps of shear, some peculiar non-monotonic behaviors are found and outlined.