In this contribution we outline polyelectrolyte (PEL) complex (PEC) nanoparticles, prepared by mixing solutions of oppositely charged polyelectrolytes, whose size and shape can be regulated by external and media parameters. An improved preparation protocol of PEC nano-particles based on consecutive centrifugation was elaborated by us resulting in better reproducibility and lower polydispersity. Experimental and simulation evidence was found, that salt and PEL concentration, pH, molecular weight and mixing order are sensible parameters for size regulation of spherical PEC nanoparticles. Using charged α-helical polypeptides also needle like PEC nanoparticles could be prepared. We outline advantages of dispersed PEC particles for life science applications due to easy preparation, graded nanodimensions and uptake/release properties towards proteins and drugs. Concerning the latter PEC nanoparticles are able to bind up to 0.3 g protein per 1 g nanoparticle. PEC nano-particles show binding of pharmaceutical drug compounds like vitamin B5 and bisphosphonate relevant for drug delivery systems.