Yemen, has continuously been a significant centre for importing and exporting hence its geographical location at the trade crossroads of the East and the West, particularly the bokhur (spice) road. Under Rasulids dominance (626-858A.H.), the commercial relationships between Yemen and different areas such as India, Egypt and Hijaz was developed and so the merchants carried the goods and products via sea routes from Yemen to Indian and Egyptian ports, and in return, importing different goods to Yemen. In addition, Yemen had also the commercial relationship with internal areas of Arabian Peninsula, especially Hijaz, by land and sea. The present article is an attempt to consider the causes of commercial development of Yemen in the Rasulids era. This study shows that in this period, Yemen was different from its prior time .It was due to the dominance of Mongols over the far East to Baghdad, that makes the commercial roads insecure and so the red sea became an alternative and safe route. It should be noticed that the role of Karemi merchants who had a disposal trade between Mediterranean sea and Indian Ocean coastlines to china via the Red sea was also developed the trade activities in Yemen.