Nonflammable binderless particleboards were manufactured from spruce and hempshives by steam explosion and hot pressing. An unpurified aqueous extract of phytic acid was employed for flame retardancy. Phytic acid is a renewable phosphorus molecule of plant origin, present in significant quantities in oilseed cakes. The effect of the steam explosion and/or the flame-retardant treatment on the mechanical properties and thermal stability of binderless particleboards was investigated. The results showed that the mechanical properties of the binderless particleboards were significantly impacted by the flame-retardant treatment in particular the swelling. For the untreated specimens, the results for swelling at the end of the test ranged from 5 % to 60 %. In contrast, the results for the treated samples ranged from 3 % to 10 %. Moreover, fire retardant treatment of the binderless particleboards reduced Heat Release Rate (HRR) and the mass loss rate, increased the residual mass fraction, resulted in lower average effective heat of combustion values, and usually resulted in longer ignition times.