Quality control of sample material (e.g. charcoal, collagen) is receiving considerable attention in the effort to obtain more reliable 14C dates. The atomic carbon to nitrogen (C:N) ratio is a useful indicator of contamination and/or degradation of bone collagen. Wool and silk are also composed of proteinaceous material such as bone collagen, and the C:N ratio may also be a useful quality indicator for archaeological wool and silk. Analyses of modern undyed, mordanted, non-mordanted, and naturally dyed silk and wool were done in order to determine a C:N range that indicates the sample quality. The C:N range can be different for every material as the amino acid composition of wool, silk, and bone collagen are distinct. The measured minimum and maximum C:N values were used to set up a C:N range of uncontamined and undegraded wool and silk. Then, the C:N ratio and 14C were analyzed of archaeological wool and silk samples. The applicability of the C:N ratio as a quality indicator for archaeological silk and wool was shown by the good agreement of the 14C dates with the presumed historical dates for the uncontaminated samples and the disagreement of the 14C dates with the presumed historical dates for contaminated samples.