Electrospinning is a well-known process for producing submicrometer fibers, which have wide applications in many fields, especially in tissue engineering scaffolds and drug-delivery systems. This paper presents the formation of drug-loaded electrospun twin fibers. The correlations between the twin fiber formation and the polymer materials or the loaded drugs were studied by using poly(l-lactide) and poly(l-lactide-co-glycolide) as electrospinning materials, and rifampin and paclitaxel as loaded drugs. Scanning electron microscopy showed that the formation of twin fibers is significantly affected by the loaded drug but not the polymer material. A possible reason for twin fiber formation was analyzed.