Objective: To determine the phenology of sunflower and its potential as forage for ruminants in a humidwarm environment. Design/Methodology/Approach: Six treatments were evaluated during the 2016 dry season, according to the number of cutting days after sowing (DAS): 65 (T1), 72 (T2), 79 (T3), 86 (T4), 93 (T5), and 100 (T6). The SYN3950 HO hybrid was planted in 540 m plots with a completely randomized block design and three replications. The following variables were measured: days to reach reproductive stages (Ri), plant height (PH) in cm, stem perimeter (SPM) in cm, flower diameter (FD) in cm, and dry matter production in stem, peduncle, leaf, flower, and total (DM t ha1 ), as well as the content of dry matter (DM), crude protein (CP), ash (A), neutral detergent fiber (NDF), and acid detergent fiber (ADF). Analysis of variance were carried out, as well as correlation between variables, mean comparison tests (Tukey, P0.05), and regression between variables and DAS. Results: There were significant differences (P0.05) between PH, FD, and DM production in stem, peduncle, flower, and total DM (t ha1 ), as well as in DM, CP, NDF, and ADF. The highest biomass yields were obtained at 100 DAS (16 t ha1 DM) with 26% DM, 12.7% CP, 21.9% A, 44.2% NDF, and 30.9% ADF. It is concluded that sunflower is an option for feeding ruminants in the study area.