The invention relates to a method for estimating the level of ethanol in a fuel injected into an internal combustion engine over a number (n) of cycles (n being an integer greater than or equal to 1). The method comprises the following steps: determination of the start of combustion of an injected fuel for each of the cycles; calculation of the average combustion start angle "?ave start" from the combustion start angles (?) recorded for all of the n cycles; determination of the end of combustion of an injected fuel for each of the cycles; calculation of the average combustion end angle "?ave end" from the combustion end angles (?) recorded for all of the n cycles; calculation of the combustion time between the combustion start time on the basis of "?ave start" and the combustion end time on the basis of "?ave end"; and deduction of the level of ethanol from the combustion time on the basis of a pre-determined model or a list of combustion times and associated ethanol levels.