Bipolaris Leaf spot disease is one of the most important sorghum leaf fungal diseases in planting regions. The aim of this research was the study of the inhibitory effect of colony growth and conidiogenesis of leaf water extracts obtained from milk thistle (Silybum marianum), cheer pine (Pinus longifolia), horizontal cypress (Cupressus sempervirens var. horizontalis), walnut (Juglans regia) and olive (Olea europea) on pathogenic fungus of sorghum Bipolaris leaf spot (Bipolaris sorghicola) in vitro. Leaves sample was collected of each plant in the middle of flowernig period and dehydrated using press board and newspapers. Amount of 10 grams of dry powder of each sample mixed with 100 mililiter sterilized distilled water and put in 65°С water bath for 24 hours. Mixtures were placed in refrigerator for 72 hours under 4°С temperature. After transmission of mixtures among filter paper, 100% concentration of water extract was prepared. Extracts were mixed with PDA (potato-dextrose-agar) culture medium using poisoned food method. Isolation and purification of pathogenic fungus from sorghum leaves samples infested by Bipolaris leaf spot disease was collected from sorghum farms in Gorgan region. Petri dishes were inoculated with a 5mm pill of seven day pathogenic fungus cultivation margin. The experiment was done factorial, using extract factor (five extracts) and concentration (zero or control and 100%), as completely randomized design with ten treatments and four replications. The average of colony radial growth in treatment and control Petri dishes on vertical coordinate axis was measured daily by milimeter ruler. Until colony completely grew up in control Petri dishes, radial growth measurement countinued. The percent of colony growth inhibitory for each extract was calculated using Abbott's formula. The results of analysis of data variance showed that there was a significant difference between experimentet treatments at statistical level (p0.01). Comparing the average treatments based on LSD test at statistical level (p0.05) showed that the most and the least inhibitory effect was respectively belonged to horizontal cypress (79.43%) and milk thistle (6.60%). Cheer pine (66.60%) and Olive (64.40%) stand in the same statistical group and walnut (34.40%) placed in another group. Suspension made of horizontal cypress, cheer pine and olive colony treatments was microscopic observed by distilled water and hemocytometer. The results showed that there were no conidium. Therefore, horizontal cypress, cheer pine and olive leaf water extracts with 100% concentration on B. sorghicola pathogenic fungus had antifungal property of more than 50% inhibitory and 100% conidiogenesis preventing in vitro.