Binderless rice straw particleboards were successfully manufactured by hot pressing at low temperatures (110 °C) while under pressure (2.6 MPa) using a three-step process. Two particle sizes were used: 0.25 to 1.00 mm and 0.00 to 0.25 mm. Three pressing times (15 min, 30 min, and 60 min) were studied. Eighteen types of boards were made. The physical and mechanical properties were assessed in accordance with the European Standards for wood-based particleboards, namely density, thickness swelling, water absorption, thermal conductivity, modulus of rupture, modulus of elasticity, internal bonding strength, and reaction to fire. Two panels exceeded the requirements for general uses. The panels had a low thermal conductivity (0.076 W/mK to 0.091 W/mK). The panels were classified in the same class as the fire retardants (class Bd0, according to EN ISO 11925-2:2002).