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Powders of various metals and boron are widely used in composite solid propellants to increase the combustion temperature and specific impulse of rocket engines. This paper presents the results of an experimental study of oxidation and ignition of ultrafine Alex aluminum powder, amorphous boron, microsized μμAl aluminum powder, and AlB2 and AlB12 aluminum borides in air. Metal and boron powders are heated and ignited by a CO2 laser in a heat flux density range of 65-190 W/cm2. It is revealed on the basis of thermal analysis data that the powder reactivity parameters are arranged in the following sequence (in descending order of activity): Alex →→ B →→ AlB12 →→ AlB2 →→ μμAl. The total specific heat release and the mass variation rate reach maximum values during the oxidation of amorphous boron and AlB12 aluminum dodecaboride. The Alex, boron, and AlB12 powders are easier to ignite in air under the action of an external radiant source. The power exponent nn in a dependence between the ignition delay time tigntign and the heat flux density tign(q)tign(q) = Aq−nAq−n for the μμAl, AlB2, and AlB12 powders are approximately the same and equal to ≈≈2.0, and it is lower and reaches nn = 1.5 and 1.0 for ultrafine Alex and boron powders, respectively.