Abstract: Objective To study the characteristics and mechanism of solid silicon microneedle arrays deliver sinomenine hydrochloride (SH) transport across hairless rat skin. Methods The amount of SH was determined by HPLC system. Hairless rat skin pretreated with microneedle arrays by hand. The side-by-side diffusion cells were used to investigate the effects of needlepoint shape, different insertion force, retention time and number of microneedles on the SH transdermal drug delivery. Histological examination of skin samples after piercing by microneedles was conducted on paraffin sections and then viewed by brightfield microscopy. Results The skin pretreated with microneedle arrays resulted in a remarkable enhancement of SH transport compared with passive difussion, the flat tipped microneedles were better than sharp tipped microneedles for enhancing skin permeability. The permeated SH increased with the enhancement of insertion force; however, as the insertion force exceeded 5.0 N the permeated SH didn’t increase obviously any more. The skin permeability enhanced with the increase of retention time, as the retention time exceeded 1.0 min, the retention time would not significantly affect the transport ability of the skin. Although skin permeation increased as the microneedles number increased, yet there was no linear correlation between them. The micro-conduits created in skin by microneedles piercing were validated by histological examination. Conclusion The microneedles were able to pierce into skin and form conduits, the formed conduits in skin greatly increased the skin permeability of SH. These results showed that the microneedle arrays may be an efficient and promising technology for transdermal drug delivery of SH.