Fire-resistance and thermal degradation were evaluated for particleboards incorporated with colemanite and common boron-based fire retardants (zinc borate and boric acid:borax mixture). The main purpose of this study was to suggest an alternative fire retardant to be used in particleboards with low cost and considerably lower environmental impact compared to common boron-based fire retardants. For this purpose, the colemanite mineral was chosen as a raw boron mineral because of its good fire performance demonstrated previously in wood-plastic composites. The test compounds were incorporated into the furnish during the particleboard manufacturing process. Fire performance tests and thermal degradation analysis were then performed in the treated particleboard specimens. Mass loss calorimeter tests were applied to determine the oxidative thermal degradation properties of the produced particleboards, whilst thermogravimetric analyses were used to evaluate the non-oxidative thermal behavior of the particleboards. The lowest peak heat release rate and the highest activation energy values were recorded for the boric acid:borax mixture-incorporated particleboards at a loading level of 10%. Overall the results showed that colemanite had a lower fire-retardant property in the particleboards compared to the common boron-based compounds tested in the study.