In this article experimentally investigations have been carried out to study the effect of the size and type particles on the thermal conductivity of micro and nanofluids. The study investigated nanofluids and microfluids which containing silver (Ag) and zirconium oxide (Zr2O3) as well as in the size and type of micro and nanoparticles in distilled water as base fluid with different particles size and concentrations. The experimental results emphasized the enhancement of the thermal conductivity due to the nanoparticles presence in the fluid greater than microfluids, also shown the effect of the particle size and concentration on the thermal conductivity. It has been recognized that the addition of highly conductive particles can significantly increase the thermal conductivity of heat – transfer fluids. Particles in the micro and nano – size range have attracted the most interest because of their enhanced stability against sedimentation and, as a result, reduction in potential for clogging a flow system. Furthermore the results showed that, the obtained thermal conductivities doubtlessly revealed that size and type particles was a key factor affecting conductive heat transport in suspensions. The aim of this article is an experimental exploration of the thermal conductivity of micro – and nano – particles and Compared with them as well as type particles and the method used in this researcher know Lee's disc technique. These results show noticeable enhancement in the thermal conductivity were evaluated to be ( 7.66 %, 2.35 %) for the Ag, Zr2O3 – distilled water nanofluid while reaches to (3.23 %,1.02 %) for the Ag , Zr2O3 – distilled water micro fluids at the concentration of (0.05 vol. %) and at the room temperature. A good agreement was found between the experimental obtained data for this paper and other results from published papers.