How Can I Measure Micro Current With Arduino?

Hi I would like to know if there is a practical way to measure micro currents for arduino. Luis

Not without external hardware, but for clarity, define "micro currents".

The measuring currents of the order x10^-6, I mean low currents

I use the uCurrent, but it seems to be out of production right now. You will need something similar.

Can I use an operational amplifier? what do you recomend me?

To measure microamperes you generally need a sense resistor and an amplifier. Here is an overview: http://circuitcellar.com/cc-blog/tips-for-measuring-small-currents/

luisemiliani02: Can I use an operational amplifier? what do you recommend me?

If you look at the page in jremingon's first link, then there is a link to the circuit diagram, and the other design files for that product. That should give you an insight into what you need to do.

luisemiliani02: Can I use an operational amplifier? what do you recomend me?

Arduino Leonardo has ADC with differential input gain of x200.

There is a post at Dorkbot on measuring uA with an instrumentation amp that might be helpful:

http://www.dorkbotpdx.org/blog/paul/measuring_microamps_milliamps_at_3_mhz_bandwidth