The present work describes the preparation, surface modification, and characterization of three different porous silicon (PSi) carriers for the acyclovir delivery. Acyclovir was loaded into these carriers and in vitro release behaviour has been studied. Such carriers were characterized by a combination of scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and X-ray diffraction. In vitro drug release studies showed slower release (up to 8 h), and immediate release (up to 3 h) from native and thermally oxidized PSI, respectively. Drug release kinetics studies of thermally oxidized PSi suggested diffusion controlled drug release whereas native PSi indicated a combination of both diffusion of acyclovir and erosion of the silicon scaffold as drug release mechanisms. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.