The principle of radiation spectroanalysis with minicomputer-controlled multi-channel analyzer system is explained. In the first part, the fundamental features of minicomputers are generally discussed with particular emphasis upon the combination with various I/O devices. In the second part, the MCA(multi-channel spectrum analyzer) system controlled by a minicomputer is explained from the aspects of both hardware and software. As for the hardware, the roles of ADC, console typewriter, paper tape I/O system, cathode ray tubes, X-Y recorder, and other auxiliary memories such as magnetic tapes and drums are discussed. As for the software, the function of system monitor is explained together with its block chart and individual software packages. The third part is devoted to the explanation of the mathematical methods for analyzing ..gamma..-radiation spectra. These include the smoothing of spectra with appropriate weighting coefficients, fitting with polynomials, and the detection of peaks by first derivative method. Some examples of spectroanalysis by these mathematical methods are presented. Recent works performed by other authors including many Japanese are also referred.