Agricultural pests are one of identified factors of crops as many botany scientists have shown, plant nematodes are one of the most important and dangerous five economic pathogens in the world due to their interaction with other organisms like fungi and bacteria. This study aimed to isolate pathogenic fungi associated with nematodes from cucumber roots and the ability to control them by bio-fungus Trichoderma harzianum and chemical fungicide topsin in Basra city in Iraq. Three types of fungi were isolated from the roots of cucumber plant infected with the nematode root pathogenic test of these fungi was carried out on the cucumber plant and the lowest proportion of seed germination was in F.oxysporum and M.phaseolina which reached to 67.60% and 75.00% respectively follow by R.solani which reached to 82.50%. The highest ratio for seedling death in F.oxysporum and M.phaseolina which reached to 18.51% and 16.66% respectively followed by R.solani which reached to 12.12% . The results showed the ability of bio-fungus T.harzianum to inhibit the growth of pathogenic fungus F.oxysporum by dual culture process, the antagonistic ratio reached to 1 in F.oxysporum according to the Bell scale. The using of bio-fungus T.harzianum in concentration 1.7 x 10⁶ in vitro lead to reduce the eggs hatching ratio and death of nematode to 23.44% and 21.46% respectively. While the use of fungicide topsin lead to reduce the eggs hatching ratio and death of the nematode to 16.66% and 15.68% respectively. F.oxysporum is completely inhibited by fungicide topsin. Also the results showed the effect of different treatments of soil contaminated with nematode root knot M.javanica and non-contaminated soil with nematode root knot M.javanica in the laboratory on seeds germination and seedling death in T.harzianum + topsin treatment, T.harzianum treatment and control which reached to 100% . While the lowest ratio of seedling death and infection severity in non-contaminated soil with nematode root knot M.javanica which reached to 0.00%. Whereas the lowest number of root knot in the same treatments in contaminated soil reached to 8, 6 and 14 knots / plant respectively. The highest plant length was in T.harzianum + topsin treatment, T.harzianum treatment and control non-contaminated soil with nematode root knot M.javanica which reached to 143.00, 135.00 and 136.00 cm / plant respectively, while roots length was 15.00, 11.00 and 13.00 cm /plant.