Fusarium oxysporum f. sp. lycopersici strains were isolated from wilted tomato plants and soil samples collected from different tomato fields in and around Karnataka. A total of 114 isolates named as (MB1-MB114) were subjected to cultural, morphological and pathogenicity studies. Significant variations existed among the isolates with respect to rate and type of growth, colony colour, mycelial growth pattern, sporulation, septation of the conidia, number and pattern of chlamydospore formation. The isolates were studied for their pathogenic variability by inoculating to five different tomato varieties by standard root dip method. The pathogenicity of the isolates could be categorized based on their virulence. The invasive growth of the isolates was assayed by injecting the conidial suspension of the isolates to tomato fruits.