Morphology, elemental chemical composition, number and distribution of egg masses of endemic caddisflies were studied in the near-shore area of Lake Baikal. Egg shape, size and density in clutches were examined by light microscopy. The elemental chemical composition of egg masses differs from that of larvae, pupae and imagines. The concentration of Mn, Br, Mo, Ba is lowest the concentration of Ti, V, Ni, Y, Ag, Cd is several times higher compared to females, Zn, U and some rare earth elements (Lu, Ho), – 1,2–1,5 times higher, Na, Al, Mn, Co, As, Mo, Cs, Gd, Ta, W, Au, Pb – 2,5–4 times lower, Bi, Ba, Ga, Ge, Si – 1,5–2 times lower. Elemental chemical composition of the egg masses as a whole is similar to that of the females supplying most of the macro and microelements for the caddisfly eggs. Average density of the egg masses varies from 469 to 4794 specimens/m2 at the water edge, exceeding 35 thousand specimens per m2 in some aggregations. The number of egg masses decreases with depth and ranges from 9 to 100 specimens/m2 at the depth of 3 m.