The in vivo tracking of adipose derived stem cells (ASCs) is of essential concern when they are used as seed cells in tissue engineering. This study explores the feasibility of using magnetic nanoparticles (MNs), a type of contrast agents in magnetic resonance imaging (M RI), to label ASCs such that the labeled ASCs could be tracked in vivo by MRI non-invasively and repeatedly. To do this, MNs of <10 nm surface-coated with oleic acid are synthesized via a high-temperature solution-phase reaction. Cytotoxicity of the as-synthesized MNs at concentrations up to 0.1 mg mL(-1) on 10(4) cells mL(-1) ASCs is evaluated by LDH release. Since only minor cytotoxicity is detected, the effects of the labeling technique on cellular behaviors and uptake by labeled cells are investigated. Cell proliferation and differentiation with and without MNs are compared. The results show that proliferation of ASCs (10(4) cells mL(-1)) labeled by MNs (0.05 mg mL(-1)) is significantly enhanced and dependent on the labeling time. The MNs are located in the vesicles within cytoplasm of ASCs. The cellular uptake reaches as high as similar to 180 pg/cell. Nevertheless, the labeled ASCs still maintained adipogenic and osteogenic differentiation. Hence, the feasibility of labeling ASCs by oleic acid coated MNs is ascertained and it was better to label the cells during their quiescent stage. The labeled ASCs can also be in vivo detected by MRI in a subcutaneous model in vivo. Further MRI tracking of the labeled ASCs in long-term follow-up would thus follow this current study.