En un contexto historico de expansion educativa, mejora de los rendimientos de la educacion y aumento de la participacion de la mujer en la actividad economica, este articulo examina y compara las pautas y tendencias en homogamia educativa en Mexico y Brasil entre 1970 y 2000. Concretamente, tratamos en perspectiva temporal y comparada las siguientes cuestiones: grado y alcance de la homogamia educativa y simetria en las relaciones de genero. Para ello utilizamos las muestras armonizadas de microdatos de los censos de Mexico 1970, 1990 y 2000, y de Brasil 1970, 1980, 1991 y 2000, puestas a disposicion por el proyecto IPUMS-International. Los resultados muestran un aumento de la homogamia entre las capas mas instruidas y una disminucion de la hipergamia femenina en ambos paises. Comparativamente, la homogamia educativa es mayor en Brasil que en Mexico, reflejo de una mayor desigualdad social, mientras que las diferencias de genero son mayores en Mexico. Educational homogamy (marriage between individuals of the same level of educational attainment) in Mexico and Brazil is declining significantly with the revolution in school attainment. In Mexico, over a mere three decades, the proportions finishing primary school doubled, rising from 40 percent for the 1931–40 birth cohort to 80 percent for those born 1961–70. In Brazil, where primary school consists of only four grades (compared to Mexico's six), the completion rate rose even more dramatically from 33 to 73 percent. Nevertheless these figures also show that in both countries sizeable fractions of the youngest generation did not complete primary schooling (one-fifth in Mexico and one-fourth in Brazil). Substantial inequalities of access to schooling persist. At the upper end of the educational spectrum, for these same cohorts the percentage of Mexican husbands with some university studies increased even more dramatically, from 5.1 to 13.2 percent and, for wives, from 1.1 to 8.3 percent. In Brazil the comparable figures are 2.2 to 5.8 percent and 0.6 to 5.7 percent, respectively. Marriage choice in both countries is strongly associated with levels of schooling completed—such as graduation from primary school, completion of basic or upper secondary, and attendance at or graduation from university. Years of schooling completed is not as salient. Thus, this research focuses on culturally significant categories rather than arbitrary number of years of schooling to compare patterns of marriage by educational attainment in the two countries. We analyze three successive ten-year birth cohorts, beginning with the 1931–40 generation, and take into consideration all marital unions, consensual as well as official. All coresident spouses in which either the husband or the wife was born between 1931 and 1970 are considered. The number of Mexican couples analyzed is 2,396,320 and Brazilian, 1,546,365. Our sources are high density integrated, anonymized census microdata samples obtained from https://www.ipums.org/international/index.html for the period 1970–2000. A series of nine log-linear models control for the unequal frequencies of various levels of educational attainment to reveal striking changes in the propensities of marriage within and between these groups. Log-odds ratios show universally positive homogamy for both countries, all censuses, and all levels of educational attainment except for one—where either the husband or the wife began but did not complete the secondary grades. (For this group, heterogamy was the rule in both countries and increased over time.) At the higher levels of educational attainment, homogamy is most extreme and is increasing in intensity over the generations, while at the lowest levels, homogamy is lower and declining slightly. Homogamy levels are much higher in Brazil than in Mexico, a finding which demonstrates the greater social inequalities in Brazil, and the fact that for Brazilians social mobility by means of education is more difficult than for Mexicans. These findings are suggestive rather than conclusive, and call for further research taking into account variables that influence educational attainment.