Mixed crop-livestock farms are widely spread in different tropical regions in the world; they contribute to food security, rural development, sustainability and poverty alleviation. The effect of scale on performance of dual purpose (DP) cattle farms was evaluated in two Mexican ecological zones: dry (DT) and wet tropics (WT). In 2011, a questionnaire of 184 items distributed into technical and social characteristics was applied to a representative sample of 3,285 farms with 50 or less cows (0.97%). The farms were classified into three groups according to their dimension: very small (1-9 cows), small (10-19 cows) and medium (20-50 cows). A general linear model (GLM) with two factors and their interactions was applied. Significant effects in dimension and ecological zone were found as well as seven interactions between both factors (p<0.05). Native pastures were used in all farms for grazing. However, small farms' herds frequently grazed on cultivated pastures and on crop residues (p<0.05). Medium farms showed the highest grazing surface, but in the WT silage and green fodder were used while in the DT dry fodders were used (p<0.001). The interactions between factors showed a bigger specialization in milk production in DT farms, whereas WT farms were more specialized in meat production. The mixed crop-livestock system in tropic region requires an increase in herd size according to farm's own productive structure, which is strongly influenced by the ecological zone. The systems would improve with the active participation of smallholders to identify and achieve best practices, higher technological adoption level and with an effective support from public and private Institutions.Additional keywords: marginalization; subsistence; dual purpose; tropics; resilience. Abbreviations used: AU (animal unit); DP (dual purpose); DT (dry tropic); GLM (general linear model); UW (unit of work); WT (wet tropic).Authors' contributions: Conceived and designed the experiments: JRQ and JAE. Performed the experiments: JRQ, JR and JAE. Analyzed the data: AGM and JP. Contributed reagents/materials/analysis tools: EA, CPH and JR. Wrote the paper: AGM, JRQ and CPH.Citation: Rangel, J.; Espinosa, J. A.; De Pablos-Heredero, C.; Rivas, J.; Perea, J.; Angón, E.; García-Martínez, A. (2017). Is the increase of scale in the tropics a pathway to smallholders? Dimension and ecological zone effect on the mixed crop-livestock farms.