Green Buildings have attracted international attention as a means of sustainable development within the current energy crisis and the deterioration of the world’s natural environment. Most countries all over the world have three problems: the amount of waste production, climate change and carbon dioxide emission and energy consumption during winter and summer. Utilizing agricultural waste requires information about the physical, mechanical and thermal properties of these materials. This knowledge helps the designer and decision maker assess the best ways to benefit from those wastes and also to avoid the hazards resulting from burning it or leaving it to deteriorate in the field. It is possible to use wastes such as barley straw, wheat straw, rice straw, oats, rye, flax, grass and perhaps sugarcane waste as a reinforcement fibres. The internal structure of a single straw is tubular, tough, and efficient. It contains cellulose, hemicelluloses, lignin, and silica with high bending and tensile strength. The tube shape is inherently stable and, with a microscopically waxy coat, slightly hydrophobic. Composites reinforced by natural fibres provides a construction with high comfort and enables homeowners and building managers to reduce energy consumption for heating and cooling. This chapter discusses the possibility of using agricultural wastes as reinforcement fibres. It focuses on four issues. First, it draws attention to the benefits of agricultural wastes as reinforcement fibres. Second, this chapter highlights physical, chemical and mechanical properties of some agricultural wastes. Third, the process of making earth blocks reinforced by natural fibres. Fourth, the use of natural fibres as reinforcement for earth plaster of straw bale buildings is discussed.