Bio-based miscanthus cementitious composites are potential promising sustainable building materials, however the organic matter and physical properties of miscanthus negatively influence their performances. In this study, physical milling treatment and heat treatments on miscanthus are investigated. Results show that the heat-treated miscanthus has a positive influence on compressive strength. The cavities of the parenchyma structure of miscanthus are easily filled with fresh mortar and tightly embedded in the mortar, resulting in the enhanced bonding interface. Besides, long fibre miscanthus (2-3 cm) has a better fibre-bridging effect than other forms of miscanthus, with an improvement in flexural strength of 24%. Physically treated miscanthus exhibits excellent heat-insulating performance, which is recommended for heat-insulating bio-mortar. The treated miscanthus significantly reduces the drying shrinkage, with a decrease of up to 25% at 90 days, compared to the untreated miscanthus. [GRAPHICS] .