As typical electrophilic substitution reactions of the 4H-pyrazolo[1, 5-a]indole derivatives, the Vilsmeier-Haack-Arnold (V.H.A.) and bromination reactions were investigated in detail and mechanisms involving the 1H-pyrazolo[1, 5-a]indoles as reaction intermediates are proposed. The V.H.A. reaction products were subjected to oxidative and reductive reactions, and a novel reduction of the conjugated system involving a double bond in the aromatic (pyrazole) ring was observed. Reaction pathways for these reactions are also proposed.