Objective       To analyze the effect of coating materials on the magnetic resonance imaging (MRI) signal intensity and relaxivity of magnetic nanoparticles (MNs) micelles.       Methods       PEG-b-PCL-MnFe

2

O

4

and PEI-b-PCL-MnFe

2

O

4

MNs micelles

which were MnFe

2

O

4

MNs coated with PEG-b-PCL and PEI-b-PCL

respectively

were examined by MRI. The MRI signal intensity of MNs micelles solution with different concentrations was observed

T

1

and T

2

relaxation time were measured

r

1

and r

2

values were calculated

and the effect of coating materials on the relaxivity of MNs micelles was evaluated.       Results       The MRI intensity of PEG-b-PCL-MnFe

2

O

4

and PEI-b-PCL-MnFe

2

O

4

solutions changed almost identically. With the increase of concentration

the signal intensity decreased in T

2

WI and T

2

*WI

and the signal intensity of PEG-b-PCL-MnFe

2

O

4

solution decreased significantly compared with that of PEI-b-PCL-MnFe

2

O

4

solution. The signal intensity of the two MNs micelles solutions increased firstly

and then decreased in T

1

WI. At the peak signal intensity

the concentrations were 0.2 mmol/L for PEG-b-PCL-MnFe

2

O

4

and 0.4 mmol/L for PEI-b-PCL-MnFe

2

O

4

and the signal intensity of PEG-b-PCL-MnFe

2

O

4

was lower than that of PEI-b-PCL-MnFe

2

O

4

at the same concentration. The r

2

value of PEG-b-PCL-MnFe

2

O

4

and PEI-b-PCL-MnFe

2

O

4

was 186.4 (mmol/L)

-1

·s

-1

and 83.3（mm

ol/L）

-1

·s

-1

and the r

1

value of PEG-b-PCL-MnFe

2

O

4

and PEI-b-PCL-MnFe

2

O

4

was 0.95 （mmol/L）

-1

·s

-1

and 1.09 （mmol/L）

-1

·s

-1

respectively.       Conclusion      Coating materials affect the MRI signal intensity and relaxivity of MNs micelles significantly.