This study analyzes the monthly totals and the time distribution of precipitation in the Jaru Biological Reserve (REBIO Jaru) and Nossa Senhora da Fazenda (FNS) from 1999 to 2006, both located in the State ofRondônia. The results of these analyzes show that REBIO Jaru presented a precipitation of 20%, on average, higher than FNS, and both sites presented a higher incidence of rainfall at the end of the day, where the FNS averaged at 18h and REBIO Jaru at 17h.