Biodegradable poly(butylene adipate) (PBA) and uracil composites were prepared via a solution and casting method at low uracil loadings in this work. The isothermal melt crystallization rate has been increased apparently in the composites by the addition of uracil, which acts as a nucleating agent for the crystallization of PBA. PBA may crystallize in the alpha- or beta-form under different conditions. During the nonisothermal melt crystallization, the alpha-form crystals of neat PBA are formed at only relatively slow cooling rate; however, the formation of alpha-form crystals can be induced by uracil in the composites at relatively faster cooling rates. The formation of polymorphic crystals of PBA may be regulated by changing cooling rate and the uracil loading, which provides an efficient way of controlling the polymorphic crystals formation and biodegradation behaviors.