A portable multi-channel system for the recording of biomedical signals is described wirelessly. Instead of using the analog time division modulation method of conversion, the digital multiplexing technique was applied to increase the number of signal channels to 4. Detailed design considerations and functional allocation of the system are discussed. The front unit was designed modularly to condition the input signal in an optimal manner. Then the microcontroller took care of the tasks of data conversion, wireless transmission, as well as provide simple preprocessing capability, such as average waveform or rectification. The low power nature of this microcontroller offers the benefit of battery operation and hence patient isolation from the system. Finally, a single-chip receiver, which is compatible with the RF transmitter of the microcontroller, was used to implement a compact interface with the host computer. An application of this portable recorder for lumbar pain studies is shown. This device can simultaneously record an ECG and two surface EMGs wirelessly, thus, it is useful for relieving the anxiety of patients designing clinical measurement. This approach, wireless measurement based on microcontrollers, could be an important trend for biomedical instrumentation and we helped make this document useful to other colleagues.