Well, i wanna use arduino in a range of temperature between -50 to 28.
So, anyone now if arduino works in this range of temperature?
Thanks,
Riccardo 
According to the official documentation (http://www.atmel.com/dyn/resources/prod_documents/doc8025.pdf), the operating temperature range is -40C to 85C. So looks like your lower end temperature is a little off spec. But l think it is likely to be OK. Of course, all other components (i.e. capacitors, etc) need to be able to withstand such frigid temperature as well.
It should be ok as long as there is not any condensation.
We are presuming that those values are in C rather than F...
Mowcius
If you're running off batteries, that may be the biggest issue with the cold.
I would use an insulated or heated enclosure or put some flexible heaters around the arduino board if I had enough power to keep it warm otherwise it may not work. Most commerical parts have -20C to 80C specs as that is a common commerical standard. Besides, plastic is brittle at low temperature. For flexible heaters, I suggest minco's kapton heaters. Some even have sticky backing for easy application.
http://www.minco.com/products/heaters.aspx?id=42
Thank you to all. Ya, obviously the temperature are in celsius degrees. Sorry.
Between, so there could be a problem with batteries? They dosen't work well with cold?
Another question...flexible heaters are very interesting but, anyone now how much does it cost? I cannot find it on the site...
Where i can find the time of discharge of batteries for arduino? (The same tempearure -50 to 30 degrees)
Where i can find the time of discharge of batteries for arduino?
Depends on what the current capacity is and what the arduino is powering as to the current draw. There are power saving measures that can help with this.
Mowcius