LJ is a Linux-based OS used in Motorola mid-end feature phones.

LJ (for LinuxJava) was started in 1999 and targeted the Chinese market first. Further generations were branded as EZX and MotoMAGX, and had a Qt-based UI. Java was used only in midlets and SIM cards, despite the name.

The original pre-EZX LJ project was renamed to MotoJUIX in its late years. It should not be confused with the cancelled JUIX project.

LJ supported only GSM/UMTS stack, so CDMA versions of the same phone models usually ran REX OS, or P2K.