The effect of using black and green tea waste extracts on the diet nutritional value was investigated with three methods of in vitro degradability, gas production, and McNiven's enzymatic digestion in the present experiment. Total phenolic compounds and total tannin for green tea extract were 20.3% and 14.8% of dry matter (DM), respectively, and for black tea were 18.7% and 12.7% of dry matter, respectively. The addition of green and black tea waste extracts reduced both gas production during incubation hours and dry matter degradability (DMD) in the diet (p < 0.05). A significantly reduced ruminal dry matter disappearance (p < 0.05) and a significantly increased post-ruminal dry matter disappearance (p < 0.05) were observed by adding black and green tea waste extracts. According to the results, the dry matter disappearance throughout the gastrointestinal tract was not significantly different between treatments. It can generally be concluded that the addition of phenolic compounds can be used depending on the nutritional strategy, such as reducing ruminal degradability and increasing rumen nutrient escape.