The present invention relates to a method of removing an Fmoc group, including a step of mixing a compound represented by the formula (I):HS-L-COOH (I)wherein L is a C1-8 alkylene group optionally having substituent(s), an amino group-containing compound protected by an Fmoc group, and a base to give a reaction mixture containing a compound represented by the formula (II):Fm—S-L-COOH (II)wherein Fm is a 9-fluorenylmethyl group, and L is as mentioned above, and an amino group-containing compound, and a step of removing the compound represented by the formula (II) by washing the obtained reaction mixture with a basic aqueous solution. According to the present invention, a removal method of Fmoc group, which can remove a dibenzofulvene derivative as a byproduct with ease, can be provided.
