By decreasing particle size of ingested forages, and thereby exposing more surface area to microbial degradation, chewing plays a key role in digestion efficiency in ruminants. However, the investigation of chewing behaviour at a fine scale, and in particular of rumination parameters such as chew number or bolus duration, surprisingly remains limited largely to applied agricultural research. The goal of the present study was to investigate seasonal effects on rumination parameters in free-ranging impalas Aepyceros melampus, an African ruminant experiencing a strong seasonality in food quality. Male and female impala increased both chew number and bolus duration in the dry season as compared to the rainy season. This is consistent with previous studies on livestock reporting an effect of food quality on rumination parameters, and with previous work on impala reporting an effect of season on food quality. The coefficient of variation in the chew number increased for both sexes between the rainy season and the dry season, consistent with the greater variability in the food items consumed in the dry season as reported by previous studies. Only males had an increased coefficient of variation in bolus duration between the rainy season and the dry season. Because females with young may increase chewing investment as compared to dry females in response to energetic costs of lactation, the heterogeneity in reproductive status among females during the rainy season (i.e. rearing period) may have resulted in heterogeneity in bolus duration, thereby interfering with the effect of the variability in the plants consumed. Rumination is an important process that seems to have been overlooked in field studies. Future studies, based on long-term data sets of marked free-ranging individuals should investigate to which extent parameters as easy to record as chew number or bolus duration could be used by managers to assess factors such as food quality and thus, ultimately, population performance in ruminants.