This study was aimed to evaluate the correlation between in vitro fermentation and in situ degradation parameters and to predict dry matter degradability and energy protein synchronization of roughage based diets. Different inclusion of roughage in diets [roughage 50% diet (R50D), roughage 60% diet (R60D), roughage 65% diet (R65D) and roughage 70% diet (R70D)] were used to determine in vitro and in situ parameters. The relationships between in vitro and in situ parameters were analyzed by simple linear regression. The gas volumes and fermentation kinetics of R50D and R65D were greater (P<0.05) than those of other diets, however the lesser values of partitioning factor for microbial protein synthesis efficiency was found in R50D. Although the nutrient disappearances, degradation kinetics and effective degradability were greater (P<0.05) in R50D in compare with R60D and R65D, the lowest (P<0.05) energy protein synchronization was observed in R50D. The significant correlation (P<0.05) were observed in all regression equations of in vitro gas volumes and in situ nutrient disappearances. The in situ effective dry matter degradability and energy protein synchronization were correlated (P<0.05) with in vitro fermentation kinetics and some estimated parameters such as short chain fatty acid and partitioning factor for microbial protein synthesis efficiency. Among the correlations, the greater accuracy could be achieved by inclusion of two or more parameters in regression equation. The results showed that in vitro gas production technique has the potential to predict effective dry matter degradability and energy protein synchronization of roughage based diets. Manuscript profile