The Upper-Scorpius association is the OB association nearest to the Sun ( 145 pc ) .
Its young age ( \sim 5 Myr ) makes it an ideal place to search for low-mass stars and brown dwarfs , as these objects should be relatively bright .
We have performed a photometric search for the low-mass members of the association , using the R , I , and Z filters .
The completeness limit is I \sim 18.5 and the saturation limit is I \sim 13 .
We obtain 138 candidate members , covering nearly the entire M spectral type range .
We find an excess of brown dwarf candidates over the number predicted by a Miller-Scalo Initial Mass Function .
In addition , we have performed infrared imaging and low resolution optical spectroscopy of selected candidates .
We find that the infrared observations confirm the spectral types obtained with the optical photometry .
Furthermore , we find H \alpha  in emission in 20 of the 22 objects observed spectroscopically .
As H \alpha  is an indicator of youth , we believe that these 20 objects may belong to the association .
One of them , UScoCTIO 128 has a very strong and constant H \alpha  line ( equivalent width : -130 à ) , and its position in the color magnitude diagram suggests that it is a brown dwarf with mass equal to 0.02 { M _ { \odot } } .
Confirmation of this and the other candidates will have to wait for higher resolution observations that can reveal spectroscopic mass indicators like Li I and gravity indicators , such as K I and the subordinate lines of Na I .