The characteristic equation is derived for the LP modes of quadruple-clad fibers. Normalized cutoff frequencies of a few lowest modes are accurately calculated and their universal curves for a variety of structure parameters are presented. It is shown that the cutoff properties of quadruple-clad libers are different from those of singly and doubly elad fibers. The height and thickness of the second cladding shoudn t be too large in order to obtain single mode operation at the interesting wavelength.