Lathyrus sativus has high potential both as food and fodder crop but can be severely infected by rust. This study assessed the resistance level of a collection of L. sativus accessions against three rust species (Uromyces pisi, U. ciceris-arietini and U. viciae-fabae) and characterized, for the first time, macro and microscopically the resistance to U. pisi. All L. sativus accessions were highly resistant to U. ciceris-arietini and to U. viciae-fabae but showed a compatible interaction with U. pisi. However, in spite of this compatible interaction, high levels of rate reducing resistance were identified with significant disease severity reduction, fitting the Partial Resistance definition. Detailed histological observations showed that resistance was mainly because of haustorium formation restriction with high-level of colony early abortion, and reduction in the haustoria number per colony. This was occasionally associated with reduction on the infection hyphae intercellular growth, in a clear example of prehaustorial resistance. Differences in germination, orientated germ tube growth and appressoria differentiation were observed but were, generally, of marginal importance to explain the observed resistance levels.