This investigation was carried out in the Nutritional Metabolism and Ruminal Laboratory, located at the Experimental Campus “La Maria,” of Quevedo State Technical University (UTEQ – Ecuador) with the objectives of determining in situ ruminal degradability of dry matter (DM), organic matter (OM), neutral detergent fiber (NDF), and acid detergent fiber (ADF), as well as of identifying ruminal pH variation in cattle fed with diets based on passion fruit flour. A complete randomized block design (CRBD) was applied with 4 treatments ((T1: 0%; T2: 10%; T3: 20% and T4: 30% inclusion of passion fruit flour substituting maize in diet), (diet components: corn, rice powder, bagasse soy, CaCO₃, Ca (H₂PO₄)₂ x H₂O and NaCl) and 3 blocks (cattle rumen fistulated) and 7 incubation times (0; 3; 6; 12; 24; 48 and 72 h). To establish the differences between treatment averages, Tukey (P ≤ 0.05) test was applied. The highest (P < 0.05) degradability within 48 and 72 DM - OM and NDF - ADF incubation hours was registered by treatments T1 and T2 (67.68; 69.10% MS - 65.40; 66.71% DM); (71.79; 74.14% OM - 69.28; 70.07% OM); T4 and T3 (86.46; 88.33% NDF - 80.44; 81.02% NDF); (53.94; 56.21% ADF - 47.86; 49.36% ADF respectively. The levels of passion fruit flour inclusion made it possible to keep a (6.3 – 6.8) pH after 12 h of incubation, what is considered adequate for aminolytics and fibrolytics microorganism growing.