Biodistribution of nanomaterials after lung exposure will be helpful to gaining an insight into the pulmo- nary toxicity. To observe distribution of C

60

（OH）

x

after lung exposure

radiolabel technique and single photon emis- sion computed tomography （SPECT） imaging was used in this experiment. The biodistribution of

99m

Tc-C

60

（OH）

x

in Sprague-Dawley （SD） rats after intratracheal instillation was studied. C

60

（OH）

x

（x=22

24） were labeled with

99m

Tc and the radiolabeling yield of

99m

Tc-C

60

（OH）

x

was greater than 93%. The

99m

Tc-C

60

（OH）

x

showed a high stability both in vivo and in vitro. Biodistributions of Na

99m

TcO

4

or

99m

Tc-C

60

（OH）

x

in SD rats after intratracheal instillation were ob- served by SPECT imaging. Unlike the distribution of Na

99m

TcO

4

a large proportion of the 99mTc-C60（OH）x was re- tained in lung

while a small amount of 99mTc-C

60

（OH）

x

penetrated the alveolar-capillary barrier

diffusing into circu- lation promptly after I.T. and distributing mainly in the liver

bone and spleen

a significant character of biodistribu- tion of nanomaterials. It seems that the ability of crossing over the alveolar-capillary barrier is dependent on size of the nanomaterials. The results provide valuable data for pulmonary toxicological study of nanomaterials.