Spread of common helminthosis in herd horses in conditions of Republic Sakha (Yakutia) on the base of coproovoscopy using Fülleborn's method and К.I. Skryabin method of full helminthological autopsy is studied. Young horses were infected with strongyle eggs on the first few days on pasture and started releasing helminth eggs with feces on the end of July. Infection peak has been registered in September. Delafondia sp., Alfortia edentatus and Strongylus vulgaris eggs have been detected at first in feces of young horses in October, December and February respectively; peak of infection has been determined in December–February, Febru-ary and April. 63,8 % of young horses were infected with Parascaris equorum at intensity of infection 13,2±1,1 expl. In some farms 100 % of horses were infected with P. equorum. The maximum P. equorum egg production has been registered in summer and autumn and was respectively 11,7 thousand and 11,2 thousand expl/day. Peak of infection was in October–December, and in winter the infection rate decreased. 70 % of horses and 80 % of young horses were infected with Ano-plocephala perfoliata in October. Application of Equisect showed a 100 % effica-cy in treatment of strongyloidosis and oxyurosis in horses. Strongyle eggs overwin-tered and remained viable in spring. P. equorum eggs don’t remain viable in win-ter.