Iron oxide nanoparticles (IONPs) were synthesized by pulsed laser ablation in liquids using three aqueous media: pure water, citrate solution, and glutathione (GSH) solution. Structural characterization indicates that all samples share a spinel-type iron oxide crystalline core, with minor contributions from more oxidized iron oxide species. Electron microscopy reveals crystalline iron oxide cores with characteristic sizes of about 10 nm, while highlighting pronounced aggregation in pure water and significantly improved colloidal dispersion in the presence of citrate and GSH, associated with surface functionalization. Magnetic measurements reveal a strong dependence on surface chemistry and aggregation. At room temperature, water-synthesized IONPs exhibit the highest magnetization (≈1.75 emu g −1 at ∼30 kOe), about 2.5–3 times larger than that of citrate and GSH stabilized samples, consistent with magnetically coupled aggregates. At low temperature, the trend is reversed, with functionalized samples showing a markedly enhanced magnetic response compared to water, indicating a dominant contribution from surface-related magnetic moments. These results demonstrate that the magnetic response of laser-ablated IONPs can be effectively tuned by controlling the aqueous medium and surface chemistry, without altering the crystalline core, offering a versatile and green strategy for designing iron oxide nanoparticles with tailored magnetic properties.