The so-called natural fluctuating process in a tunnel diode oscillator relating to the inherent noise such as thermal noise and shot noise is studied in this paper. In the case of near-sinusoidal sustained oscillation

the principal stastical characteristics of this oscillator are calculated by means of van der Pol method and correlation theory. By comparing the practical data with other types of oscillators

it is shown that the tunnel diode oscillator is of greater line width and of lower intrinsic frequency stability.