The purpose of this study was to produce environment friendly construction material using pistachio shells and urea-formaldehyde and improve its non-flammable feature by using fly ash as a flame retarder. For the production of composite particleboard, urea-formaldehyde and crushed pistachio shells were mixed at different ratios ranging 0.66 to 1.22 urea-formaldehyde/pistachio shells and dried in an oven at 333 K for 24 hours. The experimental results showed that the maximum hardness and three point bending strength were 64.7 Shore A and 1.45 N/mm(2), respectively, at urea-formaldehyde/pistachio shell ratio of 1. To determine the fire resistance, composite particleboard with optimum urea-formaldehyde/pistachio shells ratio of 1.0 was mixed with fly ash up to 20 mass % of total mass. The burning tests showed that although the maximum flame temperature of the composite particleboard without fly ash was 795 K this value decreased to 568 K with the addition of 20 mass % fly ash. This decrease resulted from the inert characteristic of fly ash at fire. It can be deduced from the burning test results that fly ash can be used in the composite particleboard as a flame retarder instead of chemicals or mineral agents. Optimum values recorded in this work may be applied to industrial applications and thus, non-flammable particle boards with fly ash can be used in interior applications.