One of the purposes of the present invention is to provide an aminoalkyl group-containing siloxane, in particular an aminoalkyl group- and polyoxyalkylene group-containing siloxane, in which an amount of a cyclic siloxane as an impurity contained is decreased, and a method for preparing the same. The present invention is to provide a method for preparing an aminoalkyl group-containing siloxane represented by the following general formula (1): (R13SiO1/2)k(R12SiO2/2)p(R11SiO3/2)q(SiO4/2)r (1), wherein R1 is, independently of each other, a hydroxyl group, an alkoxyl group, a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, or a group represented by the following formula (2), (3) or (6); —(CR2H)a—(NHCH2CH2)b—NH2 (2), —(CR2H)c—O—(C2H4O)d—(C3H6O)e—R3 (3), —(CR2H)f—(R52SiO)s—SiR53 (6); provided that at least one of R1 is the group represented by the formula (2); comprising a step of addition reacting (A) a hydrogensiloxane represented by the following general formula (9): (R83SiO1/2)k(R82SiO2/2)p(R81SiO3/2)q(SiO4/2)r (9) with (B) a compound represented by the following formula (10) and having a protected amino group: CHR2═CR2—(CR2H)a′—(NQCH2CH2)b—NQ2 (10) and optionally (C) a polyether represented by the following formula (11): CHR2═CR2—(CR2H)c′—O—(C2H4O)d—(C3H6O)e—R3 (11) and (D) a (poly)siloxane represented by the following formula (12): CHR2═CR2—(CR2H)f′—(R52SiO)s—SiR53 (12); and a step of removing the silyl group from the amino group, hereinafter referred to as deprotection, to thereby provide said aminoalkyl group-containing siloxane represented by the formula (1).