Biomaterials from mushrooms and natural fibers have been used to reduce environmental impacts. This study aimed to develop the mycelium composite from four local mushrooms, Pleurotus ostreatus, Auricularia auricula-judae, Lentinus squarrosulus, and Lentinus polychrous and three substrates derived from agricultural wastes (coconut husk, rice husk, and rice straw). The mycelia of all mushrooms were cultured on potato dextrose agar and measured for the growth for 9 days. It showed that L. squarrosulus had a colony size significantly greater than the other species. Then, L. squarrosulus was selected to form the biocomposites and tested for material properties, e.g., morphology, compressive strength, water and moisture absorption, and biodegradability. Microscopically, the mycelium colonized almost all parts of the rice husk while it colonized less in the rice straw and coconut husk. However, the rice straw absorbed significantly more moisture than rice husk and coconut husk, but the coconut husk absorbed significantly more water than the rice husk and rice straw. Moreover, the rice straw composite showed the highest compressive strength value and the greatest biodegradability according to the highest weight loss. This research provided the results of the mycelium biocomposite production and mechanical tests for future biomaterials.