This paper deals with the ultrastructure, lignin distribution and topochemistry in alkaline pulping of wheat straw. The ultrastructure of wheat straw fiber is similar to that of a wood tracheid. The lignin concentrations in various morphological regions of wheat straw are similar to the corresponding regions in birch wood fiber. But the lignin contents as a percentage of total lignin in ML and CC regions are much higher for wheat straw than for wood fibers. This study shows that there is hardly any topochemical effect during the delignification of wheat straw fiber in soda pulping process.