Textile scientists make researches for producing new types of fibers as well as modifying the existing fibers to provide new raw materials for technical textile applications. The easiest way of modifying fiber physical properties is to change the cross sectional shape of a synthetic fiber. Also, composite fibers loaded with different kinds of additives attracted the attention of researchers in the last decades for functionalizing fibers. Some other methods like coating, exhausting, padding or other novel methods can be used for the same purpose. But in these methods, the functional effect is generally not durable enough against several times of washing and abrasion. Also, these methods usually require higher consumption of water and heat when compared to composite fiber production. As a result, in this work the effect of cross sectional modification and composite fiber production were combined in the same fiber. One of the most important functional properties which can be provided by composite fiber production is antibacterial activity. Only a few research papers were published on antibacterial additive doped polypropylene fibers. In this work cupric oxide (CuO) doped antibacterial composite polypropylene (PP) fibers having different cross sectional shapes (circular, trilobal and triangular) were produced and the effect of cross sectional shape and CuO on the antibacterial activity, structural and mechanical properties of the fibers were investigated for the first time. Cross sectional and longitudinal images of composite fibers were evaluated by using optical microscope and scanning electron microscope (SEM). As the released content of active agent is an important parameter for the activity, durability, environmental and health effect of the product, the copper release from the fibers into the water media was investigated by inductively coupled plasma optical emission spectrometry (ICP-OES). Thermal analysis results showed that PP/CuO composite filaments having three different cross sectional shapes can be produced without any significant changes on thermal behavior of fibers. With the increasing content of cupric oxide, tenacities of fibers slightly decreased. Cupric oxide particles also led to some crystallinity changes. All of the composite fibers showed good antibacterial activity against Gram-negative bacterium Escherichia coli.