3 , 3 &# 34 ;, 4 &# 34 ;- tri - o - acylspiramycin i represented by the formula : ## str1 ## wherein r 1 , r 2 and r 3 are the same or different groups , and at least one of the groups is a straight or branched chain alkylcarbonyl group represented by -- coc m h 2m + 1 wherein m is an integer of 2 - 4 and the other group are straight or branched chain alkylcarbonyl group represented by -- coc n h 2n + 1 wherein n is an integer of 1 - 4 , and its pharmacologically acceptable acid addition salts .