In order to investigate the size dependence of microstructure of the AlSi10Mg alloy fabricated by selective laser melting (SLM) combined with a powder bed technique, plate-shaped AlSi10Mg alloy samples with various widths (ranging from approximately 10 mm to 0.3 mm) were produced in this study. All the fabricated samples exhibited characteristic microstructural morphologies consisting of melt pools with columnar alpha-Al grains surrounded by fine eutectic Si particles, whereas their sample sizes had a relatively small effect on the texture and average grain size of the alpha-Al matrix. However, the formation of fine Si precipitates inside the columnar alpha-Al grains was observed more often for the smaller-sized samples, which could be a possible dominant contributor to the observed softening of the sample by reducing sample size. The obtained results were utilized for discussing the size dependence of the strength of the SLM-manufactured porous alloy samples.