FIELD: organic chemistry, chemical technology, veterinary science. SUBSTANCE: invention relates to method of purification of (6-chloro-2-carbazolyl)methylmalonic acid di-(C1-C6)- alkyl ester of the formula (I) 
where Ra and Rb must be similar and taken among the group of (C1-C6)-alkyl. Method involves phase separation of spirooxyindole dimer of the formula (IV) 
from the indicated ester by treatment with glacial acetic acid at 30-110 C. Method provides producing pure purified ester with purity 99.80% by weight with 0.2% of impurities by weight or less that ensures to use its as a medicinal preparation for animals. EFFECT: improved method of purification. 4 cl
