The announcement comes on the same day that Apple is expected to unveil the next generation of its iPhone, which runs the iOS operating system that rivals Android.
"Today is a big day for Android," Hugo Barra, Android's director of product management, said in a Google+ post. "500 million devices activated globally, and over 1.3 million added every single day."
Barra claimed in June that 400m Android devices had been activated, and the growth rate was 1m per day. This means that Android is showing no signs of slowing down its advance.
The Android platform now represents 68% of the world's smartphones, up from 47% a year ago and well ahead of Apple's iOS, which has seen its share fall 17% since last year.
Android 2.3 Gingerbread remains the most dominant form of Google's mobile operating system, holding a 57% share of usage.
Since its launch last autumn, Android 4.0 Ice Cream Sandwich is now on 20.9% of handsets, and is gaining ground after a rather slow start.
Android 4.1 Jelly Bean, which launched with Google's own Nexus 7 tablet in July, is on 1.2% of devices, according to Google statistics reported by CNET.