@Mounir,

Go to Tools > Add XY data..

..... Call your excel data and then specify X and Y fields and determine the Coordinate System or import the defined Coordinate System of another layer in the extent of your study area (e.g. Boundary layer).

Save your excel as a csv file. Import that.

Dear Mounir Louhaichi

for 9.3 or lower version  Raoof Mostafazadeh  produser very right 

@ ArcGIS 10 Desktop

Add excel file by Add data button then follow below picture

after add WGS 84 Coordinate system by select button...or use import button pick from existing layer......

what is the XYZ ？if X and Y are the spatial location and Z is the value you wanted to perform interpolation. then you can  import the data as above.

You need to assure that your file is a csv file. Than you should import it and be careful regarding X and y axes. 

Thank you Luis, your recommendation is key for the geo-database to work well

The couple of Microsoft and Esri are not togetherness after office 2007.

So, notice that import " *.xlsx " will goto mistakes, using "*.xls or *.csv" instead. 

LoL...