The ribonucleic acid (RNA) was extracted from worm body, pupa and silk-gland (posterior) of Bombyx mori acording to Kirby phenol method modified by Zubay. RNA of silk worm eggs was separated by 10% NaCl extracting method after treatment of lysozyme. The ultracentrifugal method was applied to separation of soluble RNA and ribosomal RNA from silk-gland. The nucleotide composition of RNA preparations as deseribed above, was determined by ion exchange resin column chromatography. On the other hand, total RNA spinning gland of spider (Nephila clavcta L, KOCH) was prepared and its nucleotide composition was measured in an attempt to compare with that of silk-gland of Bombyx mori. Results of obtained are follows. 1) The RNA of silk worm eggs could not be separated by routine extraction method available, but was succeeded by lysozyme lysis. It is extraction process was described in detail in the text. 2) Nucleotide compositions of egg, worm body (excludes silk-gland), pupa and sillk-gland of Bonbyx mori, are summarized as follows. 도표 Pu/Py ratio of RNA worm body, pupa, and silk-gland are different among each other, while their G+U/A+C ratio arc almost identical within experimental error, ranging from 1.32 to 1.36. No such high figure of G+U/A+C value has been reported from biological materials. G+C/A+U ratio of worm body and pupa is identical and is different from that of silk-gland. Pu/Py, G+C/A+U, G+U/A+C ratios of silk worm eggs are considerablly different from those of worm body, pupa and silk-gland, and discussion was made with respect io such differences. 3) The nucleotide compositions of total RNA, ribosomal RNA and soluble RNA, and totsl RNA of spinning gland of spider are summarized as below. 도표 G+C/A+U, G+U/A-C values of gland RNA of silk worm and spider are quite different each other, while Pu/Py ratio of glands of both species is identical. The great difference was observed conscerning Pu/Py and G+C/A+U values between soluble RNA and ribosomal RNA of silk-gland, but G+U/A+C ratio of RNA of two groups is identical. 4) It is remarkable fact that the RNA nucleotide composition of Bombyx mori changes during its ontogenetic process (from oval life to pupal one) with special difference to Pu/Py and G+C/A+U ratios. The RNA nucleotide pattern of Bombyx mori tissues belongs to GC-type with 1.3 of G+U/A+C ratio, which such high value has not yet been reported among microbial, algae and plant kingdoms.