¹Department of Animal Science,University of Mohaghegh Ardabili, Ardabil, IRAN DOI : 10.9775/kvfd.2017.18187 This study was conducted to determine effect of adding ZnO nanoparticles at levels of 0, 30 and 60 ppm on in vitro gas production of some animal and plant protein sources. In this study, gas production at 2, 6, 12, 24, 48 and 72 h incubation were measured and 200 mg of samples were used for gas production analysis. The results showed that after 72 h of incubation, the most volume of gas production in the plant protein sources of soybean meal (SM) and in between the sources of animal protein in poultry offal meal (POM) were respectively 58.23 and 28.34 mL per 200 mg of dry matter was obtained. In related with the parameters of nutrition from incubation data, metabolizable energy (ME), for soybean meal at the levels of zero, 30 and 60 ppm ZnO nanoparticles added to the 8.55, 8.81 and 7.54 were highest and for blood meal (BM) were lowest 2.26, 2.31 and 2.01 MJ/kg dry matter (DM), respectively. The highest and the lowest amount of organic matter digestibility (DOM), short-chain fatty acids (SCFA) and microbial protein (MP) were also for SM and BM. Overall, the results showed that using levels of 0, 30 and 60 ppm of ZnO nanoparticles was no effect on in vitro gas production of some animal and plant protein sources but had no significant effect in some hours of incubation, gas production and nutrition parameters. Keywords : In vitro gas production, Nutrition parameters, Protein sources, ZnO nanoparticles