The construction industry is in a quest for low-cost eco-friendly materials with very good properties required for building construction such as Agrostone. It is made of magnesium oxychloride cement and fillers for reinforcement. In the present work, experimental studies are made on compressive strength of Agrostone made of different bio-fillers like water hyacinth, bagasse and grass to identify a low-cost bio filler that gives the required properties. It is also aimed to replace the presently used fillers with water hyacinth refuse from Lake Tana, Ethiopia to reduce cost and disposal problems. The specimens are casted as per ASTM C109 standard of 50 mm cube from the three bio-fillers. Twenty-four specimens are prepared for each type and six specimens are selected randomly from each of the three groups with a curing time of 7, 14, 21, and 28 days. The compressive strength of specimens is tested as per ASTM C90 based on the peak load. The average values of compressive strength for water hyacinth Agrostone are 5.26 MPa, 5.34 MPa, 5.52 MPa, and 6.4 MPa at 7, 14, 21, and 28 days of curing, respectively. Agrostone made of bagasse and grass bio-fillers have higher compressive strength compared to that of water hyacinth. The water hyacinth Agrostone specimens after 28 days of curing have comparable strength of class AAA hollow concrete block (5 MPa) of Ethiopian material code. The strength to mass ratio of water hyacinth Agrostone is superior to those of bagasse and grass. The cost of building partition walls using water hyacinth Agrostone will be reduced by 53 % compared to plastered and painted hollow concrete block wall of the same thickness.