Provided are an oil condition determination system and an oil condition determination method that are capable of continuously determining the oil condition when oil is partially replaced or oil is added. An oil condition determination system includes a measurement unit and a determination unit. The measurement unit periodically measures a resistance value of oil. The determination unit periodically determines a condition of the oil based on the resistance value, stores a local maximum value of the resistance value, determines that the condition of the oil has changed when a difference between the local maximum value and the resistance value becomes greater than or equal to a first threshold value, and initializes the local maximum value and updates the first threshold value when the amount of change in the resistance value per unit time becomes greater than or equal to a second threshold value.