| Summary: | The present study aims to establish the relationship between chemical composition and in vitro methane (CH<sub>4</sub>) production of high Andean grasses. For this purpose, eight species were collected in dry and rainy seasons: <i>Alchemilla pinnata</i>, <i>Distichia muscoides</i>, <i>Carex ecuadorica</i>, <i>Hipochoeris taraxacoides</i>, <i>Mulhenbergia fastigiata</i>, <i>Mulhenbergia peruviana</i>, <i>Stipa brachiphylla</i> and <i>Stipa mucronata</i>. They were chemically analyzed and incubated under an in vitro system. Species such as <i>A. pinnata</i> and <i>H. taraxacoides</i> were characterized by high crude protein (CP. 124 g/kg DM) and low neutral detergent fiber (NDF. 293 g/kg DM) contents in both seasons, contrary to <i>Stipa</i> grasses. This same pattern was obtained for <i>H. taraxacoides</i>, which presented the highest values of gas production, organic matter digestibility (DOM), metabolizable energy (ME) and CH<sub>4</sub> production (241 mL/g DM, 59% DOM, 8.4 MJ ME/kg DM and 37.7 mL CH<sub>4</sub>/g DM, on average). For most species, the content of CP, acid detergent fiber (FDA) and ME was higher in the rainy season than in the dry season, which was the opposite for CH<sub>4</sub> production (<i>p</i> ≥ 0.05). In general, the nutritional content that most explained the behavior of CH<sub>4</sub> production was the NDF content (R<sup>2</sup> = 0.69). Grasses characterized by high NDF content produced less CH<sub>4</sub> (R = −0.85).
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