The regulator has imposed some Islamic business units to do the spin-off after the enactment of the Islamic banking act (The Act No. 21 of 2008). This paper examines the relationship between spin-off, market structure, and deposit funds. It uses panel data regression for analysis. The result shows that there is a difference in deposit funds between the spin-off banks and non-spin-off banks. The result also indicates that there is a relationship between spin-off, market structure, and deposit funds in the Indonesian Islamic banking industry. It implies that the regulator should a policy to accelerate the Indonesian Islamic banking industry.