The presented paper is part of the complete description of fluid-dynamic conditions in the selected static mixers: Koflo and Kenics. The research was also performed for an empty pipe used as a reference state. The scope of work included the analysis of the residence time distribution in the mentioned devices for different Reynolds numbers for both laminar and turbulent flow regimes. The report contains a discussion about residence time distribution function E(t), cumulative distribution function F(t), as well as the parameters like the mean residence time tm and the variance sigma(2). The main aim of the presented work was to show the applicability of static mixers as chemical reactors and to present their operation characteristics to evaluate the derogations distinguishing them from well known ideal states (i.e. plug flow or ideal mixing). As a result of the accomplished study it was proved that Reynolds number increase results in narrower RTD in all of the tested devices, however the fluid motion is far from plug flow due to axial and radial mixing and the considered equipment should be treated as non-ideal reactors requiring some additional models for the right description. What is more, in the case of laminar flow, the Kenics static mixer showed the narrowest spread and was considered as the best solution among the studied devices. In the turbulent flow, the difference between E(t) functions for all of the mentioned equipment was so small that the suggestion of small impact of insert type on the RTD was made.