A silicon-containing copolymer is disclosed which has a number average molecular weight of 500-100,000 and which contains the following structural units (I)-(III): ##STR1## wherein R.sup.1, R.sup.2, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 each represent an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an aralkyl group, an alkylamino group or an alkylsilyl group and and R.sup.3 and R.sup.8 each represent a divalent aromatic group. The copolymer is produced by reacting an organodihalosilane, a disilyl compound, a diamine and ammonia with each other.