Purpose: Among the members of the DOCK family, DOCK1-5 function as guanine-nucleotide exchange factors for small GTPase Rac1, which regulates the actin cytoskeleton. It has been reported that in model organisms the Dock-Rac axis is required for myoblast fusion. We examined the role of DOCK1-5 in trophoblast fusion herein. Methods: We used a quantitative polymerase chain reaction (qPCR) to examine the mRNA expressions of DOCK1-5 and differentiation-related genes, i.e., fusogenic genes, in human trophoblastic cell lines, BeWo and JEG-3. We treated BeWo cells with TBOPP and C21 to inhibit DOCK1 and DOCK5. Cell dynamics and cell fusion were assessed by live imaging and immunostaining. The signaling pathways induced by DOCK1/5 inhibition were examined by western blotting. Results: DOCK1 and DOCK5 were expressed in BeWo cells. The inhibition of DOCK1 or DOCK5 did not prevent the cell fusion induced by forskolin (a common reagent for cell fusion); it induced cell fusion. DOCK1 inhibition induced cell death, as did forskolin. DOCK1 and DOCK5 inhibition for 24 and 48 h increased the expression of the genes ASCT2 and SYNCYTIN2, which code responsive proteins of trophoblast cell fusion, respectively. Conclusion: DOCK1 and DOCK5 inhibition participates in BeWo cell fusion, probably via pathways independent from forskolin-mediated pathways. (c) 2020 Elsevier Inc. All rights reserved.