The company is testing the feature in its AOL 5.1 beta, company spokesman Anne Bentley confirmed.
Bentley said: “At present, the beta client allows AIM users to add AOL ICQ users to their Buddy Lists view when online, and to send them instant messages. It's not yet a complete communications circle - although ICQ users can receive messages from AIM users, they cannot yet add them to their Buddy Lists.
“Hopefully the next version of ICQ would support AIM users.
MacCentral claims AOL hopes to offer the same functionality to iChat users in future, but that this feature is currently in early-stage testing.
The move comes as the company faces increased competition from rival services, such as Yahoo's Messenger and MSN Messenger.
AOL acquired ICQ from Israeli firm Mirabilis in 1998. While AIM has become popular with US users, ICQ has been adopted by the international market.
By enabling its two services to communicate together AOL could increase its user base.