2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/80634This paper presents the perturbation theory for the double--sine--Gordon equation. We received the system of differential equations that shows the soliton parameters modification under perturbation's influence. In particular case $λ=0$ the results of the research transform into well-known perturbation theory for the sine--Gordon equation.LaTeX, 7 pages, 3 figuresPattern Formation and Solitonstext