Abstract： Objective To investigate the labeling rate with poly-L-lysine (PLL) and super paramagnetic iron oxide particles (SPIO) for C6 rat glioma cells and the impact of PLL and SPIO on labeled cell bioactivity. Methods C6 rat glioma cells were incubated without SPIO or PLL (control group), with 25 mg/L SPIO (group A), 25 mg/L SPIO+0.75 mg/L PLL (group B), and 50 mg/L SPIO+1.5 mg/L PLL (group C) , respectively. The labeled cell bioactivity was analyzed by MTS assay (mono-nuclear cell direct cvtotoxicity assay) at different incubation time (6, 24 and 48 h) after treatment, and the labeling rate was detected by Prussian Blue staining. The labeled cells mass were imaged in vitro using a 3.0 T MRI scanner with GRE/30° T2*WI sequence. The R2* values and signal intensity were compared among these groups. Results Up to 48 h post-labeling, there was no significant decrease of cell bioactivity in all labeled cell groups (all P>0.05). Prussian Blue staining showed that the labeling rate was >98% in group B and C compared with about 70% in group A. The staining appeared increasingly darker in SPIO/PLL mixed labeled cells along with higher concentration of SPIO. 3.0 T MRI was signal-sensitive for the labeled cells. The R2* values were 11.76±5.74, 12.13±4.39, 61.22±27.85 and 90.07±35.59 for control group and group A, B and C, respectively. Difference of R2* value was not found between control group and group A (P>0.05), but was found between group B and C, meanwhile R* values of group B and C were significantly different with control group and group A (all P<0.01). Conclusions PLL may enhance the efficiency of SPIO labeling for C6 glioma cells and has no significant impact on the cell bioactivity. 3.0 T MRI with GRE/30° T2*WI sequence is signal-sensitive for labeled cells in vitro. The R2* value may increase along with intracellular SPIO level. 25 mg/L SPIO+0.75 mg/L PLL may yield satisfactory labeling for rat C6 glioma cells in vitro.