The phase diagram of molecular alloys of n-tetracosane (n-C24H50) and n-hexacosane (n-C26H54) has been established by a joint thermodynamic and structural study of twenty five compositions. At "low temperatures" it shows the existence of two limited domains of terminal solid solutions gamma(0)(C-24) and gamma(0)(C-26) and of three orthorhombic intermediate phases, denoted beta’(1), beta " and beta’(2). With increasing temperatures, these five solid solutions undergo the same solid-solid transitions as those observed in the even-numbered and odd-numbered pure n-alkanes and in the system n-docosane (n-C22H46)-n-tetracosane (n-C24H50), i.e. : gamma(0)(C24) and gamma(0)(C-26) --> Rotator phase alpha-RII (R(3) over barm$) --> Liquid beta’(1), beta’(2) and beta " --> Rotator phase beta-RI (Fmmm) --> alpha-RII --> Liquid xt