Portable bioimpedance spectroscopy (BIS) devices are of great value for monitoring the pathological status of biological tissues in clinical and home environments. The two traditional techniques for measuring complex bioimpedance, the bridge method and quadrature demodulation method, are either time-consuming or often associated with high cost, high power consumption, and large board space, and therefore are not ideally suitable for designing a portable device for BIS measurement. This paper describes a novel design of a portable BIS device based on the magnitude-ratio and phase-difference detection method and its implementation using the newest generation of analog electronic products which greatly decrease the complexity of both hardware and software. In order to improve the accuracy of the device, a three-reference calibration algorithm was applied. Experimental sweep-frequency measurements on RC circuits were carried out to preliminarily evaluate the performances of the device. The results obtained by the device were found to be in good agreement with the results measured by a commercial impedance analyzer HP4194, with an overall mean error of 0.014% in magnitude and 0.136 degrees in phase over a frequency range of 20 kHz to 1 MHz.