The size of the secondary phases affects the lanthanum-doped titanium‑zirconium‑molybdenum (La-TZM) alloy properties. In this study, the microstructure and mechanical properties of the La-TZM alloys were regulated by adding carbon and Ti/Zr elements, which resulted in different secondary phase characteristics. Adding nano-TiC and ZrC decreased the micron secondary phase size of the La-TZM alloy by 26.7%, and increased the yield strength by 27%, reaching 1239 MPa. The effects of secondary phase size and distribution on yield strength were analyzed. This study contributes to the design and theoretical analysis of new molybdenum alloys. • Average size of micron secondary phases doped nano-TiC/ZrC is reduced by 26.7%. • The yield strength of doping nano TiC-ZrC alloy improved 22.6%, reaching 1239.42 MPa. • The effect of secondary phase size on yield strength were calculated. • The effect of secondary phase distribution on grain size were analyzed. [ABSTRACT FROM AUTHOR]