The purpose of this study was to determine the ruminal degradability of dry matter of fodder of highland Costa Rica corn. The crop was planted with 50 kg of seed/ha, with 70 cm between rows, 50 cm between plants and three seeds in each hole. The first sampling was taken after 37 days and every two weeks thereafter, through 149 days. The potential degradability of the dry matter of the leaves, stems and the corn ears was determined. The potential degradability of the whole plant diminished from 93% to 74% as the age of the plants increased during the first 90 days. In the stem, the soluble part diminished from 40% to 27%, while in the leaves it remained constant between 15% and 16%. The degradable part of the stem diminished from 55% to 43% during the growth of the plant, and the leaves varied between 67% and 74%. The degradability rate of the stem was above 5% /h through 65 days and in the leaves it was lower. From the 79th day on, the leaves had a degradability rate above 5%/h and the stems had low rates. After the 107 th day the ears had a potential degradability of 85% and a degradability rate of 7.5%/h.