Since petroleum production began, pollution of natural environments by crude oil and its products had been devastitating; exposure of microorganisms to the crude oil contamination could have some measurable effects on soil microbial community and in turn alter soil fertility. This study therefore focused on the response of fungi to diesel oil contamination in a soil. Soil samples (3kg weight) were contaminated with 90ml, 180ml, and 270ml volumes of diesel oil; uncontaminated soil (0ml volume) served as control. Microbiological analysis of the soil samples was carryout on saboraud dextrose agar and mineral salts oil ager at days 1, 7, 14 and 21 intervals after addition of diesel oil to the soils. Mean counts of heterotrophic fungi (X103CFU G-1 soil) were: 0ml, 7.0, 90ml, 4.5, 180ml, 4.5, and 270ml, 4.0. Mean densities of hydrocarbon-utilizing fungi (X102CFU G-1 soil) for 0ml, 90ml, 180ml, and 270ml soil options were: 5.0, 3.5, 6.8 and 3.0 respectively. Fungal organisms isolated include Aspergillus niger, Aspergillus species, Fusarium species, Mucor species, Rhizopus species and Saccharomyces species, which occurred in control soil and polluted soils but Mucor species did not occur in 90ml soil option. The study showed that heterotrophic fungi responded negatively to addition of diesel oil to soil while hydrocarbon-utilizing fungi showed both positive and negative response depending on the volume of diesel added to soil. Occurrence of fungal organisms in polluted soils explained the fact that fungi are capable of utilizing diesel oil and can be used in cleanup operations in crude oil spillage sites.