Effect of acetic acid vapours on tomato root rot fungi under laboratory and greenhouse conditions was studied. Acetic acid vapours at four concentrations i.e.0.0, 2, 4 and 6 µl/L were tested against linear growth of F. solani, R. solani and S rolfsii. Results revealed that complete inhibition in linear growth was obtained with AA at 6 µl/L for all tested fungi. The most sensitive fungi to acetic acid vapours are F. solani and R. solani which inhibited at 4 µl/L, while S. rolfsii were more resistant to acetic acid vapours at 6 ^l/L caused the complete inhibition of linear growth. Complete inhibition of chlamedospores of F.solani was obtained by AA vapour at 15 µl/L while, Sclerotia of S. rolfsii showed more resistance to acetic acid vapours as their germination was completely inhibited at 20 µl/L of acetic acid vapour. Under greenhouse conditions results indicated that complete reduction in total count of pathogenic fungi was obtained with AA at ^l/L for F. solani & R. solani and at 100 µl/L for S. rolfsii. The highest reduction was achieved with AA at 25 µl/L which reduced the population by 74.0, 84.0 and 53.0% for F. solani, R. solani and S. rolsii respectively. All tested concentrations of AA significantly reduced the percentage of root rot incidence of tomato plants . The most effective concentration of acetic acid vapour was 100 µl/L which reduced the disease incidence by 92.9, 94.2 and 93.9% for F. solani, R. solani and S. rolsii respectively. It could be suggested that acetic acid vapours might be safely used for controlling tomato root rot disease under greenhouse conditions.