In this paper, we report the influence of reaction conditions and the chain length on the nanoparticle (NP) size and morphology for thermal decomposition of long-chain iron carboxylates such as Fe(III) oleate, palmitate, and myristate. In the majority of cases, spherical NPs are obtained; however, nonspherical morphologies were observed in some "extreme" conditions. For example, iron oxide nanostars are formed in eicosane at the Fe oleate/oleic acid ratio of 0.49 g/mL: the highest oleic acid content when NPs still form. The cubic NPs with flat facets are obtained by decomposition of iron palmitate at the lowest palmitic acid fractions, but the most monodisperse cubes are formed at the Fe palmitate/pahnitic acid ratio of 1.19 g/mL. Elliptical NPs are formed from Fe myristate with the most well-defined structure. Easy transformation of these NPs from wustite to maghemite without aggregation and loss of solubility makes them excellent candidates for biomedical applications after proper functionalization described in our preceding papers.