The objective of this investigation is to evaluate impacts of some chemical and biological treatments on the chemical composition, cell wall constituents and in situ degradability of olive cake (OC). OC was treated by water (control, T₁), 8% molasses (T₂), 7% urea (T₃), 8% molasses + 7% urea (T₄), 8% molasses + 1.5% sodium hydroxide (T₅), 8% molasses + 3% sodium hydroxide (T₆), 8% molasses + 6% lime (T₇), 8% molasses + 8% lime (T₈), 8% molasses + 10% lime (T₉), 8% molasses + 0.25% Cata pro^® (T₁₀),  8% molasses + 0.5% Cata pro^® (T₁₁) and 8% molasses + 1% Cata pro^® (T₁₂). The initial moisture in all treatments was adjusted at 65%. The obtained results revealed that the chemical and biological treatments of OC for 30 days had positive advances on the chemical composition of OC, where the crude protein values increased, while the crude fiber contents decreased. The best improvements were occurred by adding molasses with lime (T₉) or with 1% Cata pro^® (T₁₂). Also, the neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL) and total tannins decreased with all treatments. T₉ recorded the least content of cellulose, however the lowest percentage of total tannins was observed with T₆. Among the biological treatments of OC, the maximum reduction in cellulose content accompanied by the minimum concentration of total tannins was detected with T₁₂. All treatments led to improve crude protein, disappearance of NDF, ADF and ADL after 24 and 48 hours of the in situ degradability of OC. The T₉ and T₁₂ were the most effective treatments. Conclusively, the best improvement of chemical composition, cell wall constituents and in situ degradability of OC were occurred by 8% molasses + 10% lime (T₉), followed by 8% molasses + 1% Cata pro^® (T₁₂).