The nickel-based superalloy CM186LC is dedicated to directional solidification processes. The withdrawal rate is an important parameter of directional solidification that can be used for microstructural tuning and consequently, an improvement in the properties of the alloy. In the present work, the effect of the withdrawal rate on microstructure of the CM186LC alloy is investigated. Herewith thin-walled specimens (0.4 mm and 2.0 mm) with grain selector were used to verify single crystal castability through the Bridgman process. The results show that slower withdrawal rates reduce the primary dendrite arms spacing. Samples with thickness of 0.4 mm showed smaller primary dendrite arms spacings than samples with 2.0 mm. Monocrystalline microstructures were obtained only with withdrawal rates equal or slower than 3 mm/min. Above 3 mm/min, polycrystalline and columnar microstructures were formed.