"An Laboratory experiment was carried out in the Department of Horticulture and Landscape Gardening - Faculty of Agriculture - Diyala University for the spring season 2017 in order to study the inhibitory effects of some plant extracts on the laboratory growth characteristics of the Tomato seeds, using Petri dishes designed in Completely Randomized Design ( CRD) in three replicates to study the effect of three different concentrations (zero , 50% and 100%) of water extracts of onion, Blady grass, Nut grass and Johnson grass in the percentage of seed germination of Tomato seeds and the growth rate and some other growth characteristics of theTomato seeds. The experimental results can be summarized as follows, Plant extracts affected For each of the onion, Blady grass, Nut grass and Johnson grass and the concentrations used, and interferences between them, have a significant effect in all studied traits of Tomato seeds the treatment resulted in the plant extract of Nut grass and Johnson grass On the occurrence of high and clear inhibitions in all the studied traits of the tomato seeds, while the other plant extracts varied with the degree of inhibition.