Nonylphenol (NP) belongs to the class of endocrine active substances and are of special importance due to their high longevity and toxic characteristics. Nonylphenol is a multi-compound mixture that becomes generated as a by-product after degeneration of nonylphenol-ethoxylates (NPE) due to biological wastewater treatment. NPE are components of several cleaning agents, emulsifiers, dispersing agents and pesticides. NP is a mixture that consists mainly of para-substituted mono-alkylphenols with different isomeric nonyl-groups. Despite their high persistence and toxicity, exposure to NP induces alterations of the endocrine homeostasis in water organism, bird and mammals. NP can potentially bind to different hormone receptors (e.g. estrogen receptors, progesteron receptors and androgen receptors) and induce or modulate hormone-dependent downstream pathways. The influence regarding the reproductive fitness is much higher in females compared to males.