This paper presents a low-power RF-transmitter for intelligent healthcare systems. With attention to power-efficient communication in the local sensor network, the required low-power integrated circuits (ICs) are developed for a healthcare system with miniaturization and system integration. A quadrature CMOS voltage-controlled oscillator and a direct-conversion transmitter with PA and up-conversion mixer have been implemented to fit the specification of the IEEE 802.15.4 2.4 GHz standard. The low-power ICs of the transmitter have been applied in the TSMC 0.18-μm CMOS standard process. The measurement results reveal that the transmitter IC can fit in with the link budget of the UHF ZigBee system for healthcare applications.