A method was developed based on the measurement of the apparent modulus of the elasticity of plums, using a cylindrical probe and a force of 1 N. This method is extremely sensitive and is fully nondestructive. The measurements are taken using an Instron Universal Testing Machine. The results obtained correlate very well with other objective quality indices and sensory tests. The method was verified on several plum cultivars. This method is suitable in estimating the different grades at which any particular fruit has ripened by the day of picking and during storage and may be used to establish the firmness of the plums from the point of view of the consumer. It was found that fruit of the Dąbrowicka, Amerf and Valjevka varieties should have - at the consumption stage of maturity - an apparent modulus of elasticity ranging from 0.100 to 0.250 MPa (optimum at 0.150 MPa), when measured using a 6 mm probe and when recalculated using a 4 mm probe, respectively 0.071-0.217 MPa (optimum at 0.120 MPa).