The effect of soft rot disease of sweet orange fruit on its nutritional and market values in Ogbomoso, in the humid forest of Southwestern Nigeria is being investigated. Result of the investigation revealed that Penicillium digitatum was responsible for the soft rot diseases of sweet orange fruit. Eighty percent of the sweet orange fruits were found infected with soft rot disease and over 50% of the fruit produced on those fruits were severely infected. The 8 non-infected sweet orange fruit was significantly (P≥0.05) higher than the soft rot infected sweet orange fruit in carbohydrates, crude fibre, ash, protein, calcium, iron and phosphorus content. In addition, a significant (P≥0.05) reduction in the price of sweet orange was found to be associated with soft rot infected fruit in all the three major market surveyed. The significance of the effect of soft rot disease of sweet orange fruit on its nutritional and market values in Ogbomoso, Nigeria.