We present an adaptive slicing scheme for reducing manufacturing time of 3D printing system. Based on a new saliency based metric, our method optimizes the thicknesses of slicing layers to save the printing time and preserve the visual quality of printing results. We formulate the problem as a constrained `0 optimization and compute the slicing result via a two-step optimization scheme. To further reduce the printing time, we develop a saliency based segmentation scheme to partition an object into subparts and then optimize the slicing of each subpart separately. We validate our method with a large set of 3D shapes ranging from CAD models to scanned objects. Results show that our method saves 30-40% printing time and generates 3D objects that are visually similar to the ones printed with the finest resolution.