Purpose: To evaluate the effects of intravitreal silicone oil (SO) on subfoveal choroidal thickness (SFCT). Methods: A total of 60 patients with unilateral pseudophakic macula-off rhegmatogenous retinal detachment were treated with a three-port pars plana vitrectomy and a 5,700-cSt SO endotamponade and subsequent SO removal. SFCT was measured before and 3 months after SO removal. The main outcome measure was the difference between the SFCT of operated eyes and the fellow eyes. Results: Before SO removal, the mean SFCT differences in group 1 (3–6 months’ duration of SO), group 2 (6–9 months’ duration of SO), and group 3 (9–18 months’ duration of SO) were –14.8, –25.5, and –62.1 µm, respectively (p = 0.002, r = 0.398). Three months after SO removal, the mean SFCT differences in group 1, group 2, and group 3 were –13.4, –23.3, and –59.0 µm, respectively (p = 0.002, r = 0.393). Conclusion: SFCT decreased significantly in eyes with long-term (≥6 months) intravitreal SO tamponade. Choroidal thinning did not improve after SO removal.