The objective of this study was to determine the different morphotypes of Fusarium oxysporum present in the root of Xanthosoma sagittifolium and evaluate the effect of alcoholic extracts of Psidium guajava on their in vitro inhibition. Strains of Fusarium oxysporum were collected in eight localities where X. sagittifolium is grown. Fusarium strains isolated from roots of X. sagittifolium harvested in each locality were grown on PDA medium. The antifungal test was evaluated using ethanol extracts from P. guajava leaves at 30 and 60%. The virulence test of each strain on young plants of X. sagittifolium aged three months were realized. Eight strain of Fusarium oxysporum were successfully isolated. After maximum growth, five morphological types were observed (pionnotal, sclerotic, clowny, cottony and ras senescent). The cottony strain was abundant and present in all the locality. Histological analysis of the different strains obtained revealed the presence of septate or siphoned hyphae and three types of conidia (microconidia, macroconidia and sporangiospores or chlamidospores). The inhibition tests were very high with 60% of ethanol extract of P. guajava, and 83.33% of inhibitory effect were observed after eight days of growth, in the strains collected in X. sagittifolium roots, in L3 (Loum) and L4 (Bangoua) localities. After infection of X. sagittifolium plants with each strain of F. oxysporum isolated, symptoms observed were yellowing and wilting of leaves. However, plants inoculated with the L3 (Loum) strain showed both yellowing and wilting of leaves. The application of ethanol extracts from P. guajava leaves reduced the severity of the disease in the inoculated plants after 14 days. These results obtained showed that F. oxysporum is not only saprophytic fungi, it’s also able to induce yellowing and wilting of leaves in X. sagittifolium.