The aim of the present study was to improve the toughness of a powder-metallurgically produced aluminium matrix composite (AMC) with a constant reinforcement content. For this purpose, the influence of the particle size and size distribution of the metal matrix powder on the mechanical properties was investigated. In this context, as-received metal matrix powder (d₅₀ = 40 µm) and three further fractions sieved from the as-received powder: fine (d₅₀ = 25 µm), coarse (d₅₀ = 52 µm) and bimodal (50 wt% fine + 50 wt% coarse, d₅₀ = 36 µm), each mixed with 35 vol% SiC_p, were consolidated into AMCs by field-assisted sintering technique. Due to the small sample size, the tensile test was chosen to assess the toughness. The area under the stress-strain curve until failure was calculated as energy absorption capacity (toughness). The use of the fine matrix powder fraction leads to an increase in toughness of 70% compared to the as-received condition. This is mainly due to the high bulk density of the fine powder fraction. Furthermore, it was found that the consumed heating energy of this composite was almost one-third lower compared to using the as-received matrix powder. With a less significant effect, an improvement in mechanical properties can also be observed in AMCs with bimodal powder mixture. Due to low density of the powder fraction, composites made of coarse fraction showed opposite tendencies. However, it was found that it is not the average powder size of the metal matrix powder but a critical amount of fines that influences the occurrence of voids and thus the mechanical properties.