This research aims to study the water hyacinth fiber inside high density cement fiber board. By using ratio components among cement : fine sand : water hyacinth fiber : water : catalyst accelerated the formations of cement (aluminum sulfate (AI2 (SO4) 3) calcium chloride (CaCl2) sodium silicate (Na2SiO3)) on the ratio 1: 0.2: 0.075: 0.3: 0.03 by weight of total water hyacinth fiber. The 5 ratios consist of 0.0 (A1 D1 formulae) 0.025 (A2 B2 C2 D2 formulae) 0.050 0.03 (A4 B4 C4 D4 formulae) and 0.1 (A5 B5 C5 D5 formulae) by weighted all fibers were treated with sodium hydroxide solution (NaOH) at a concentration of 12%. The fiber to solution ratio was 1: 10 boiled in open system at 100 °C for 1 - 3 hours. By compressing the mixture cast machine at normal temperature (30 - 35 °C). Use a density of 0.75 g / cm3. From the test results the ratio B4 is the appropriate ratio. Can pass TIS 878- 2537 Cement Board: high density and physical properties mechanical properties and thermal insulation are good. Accelerate the formation of the most suitable cement is calcium chloride (CaCl2)