The aim of this study was to determine the effects of using 5%, 10%, and 20% of safflower (Carthamus tinctorius L. Dincer; without thorns) grain, and its hay and straw, on the in vitro fermentation parameters in the diets of horses and ruminants. The addition of up to 5% of crushed safflower grain to a horse's diet had no negative effect on the in vitro total gas production, true dry matter digestion (T-DMD), metabolic energy (ME), gas yield at 24 h (GY(24)), partial factor (PF24), microbial crude protein production (MCP) and short chain fatty acid composition (SCFA) of digestion fluid; however, increasing the grain content negatively affected certain parameters (p<0.05). The hay and straw at 5%-20% ratio in a horse's diet had a positive effect on in vitro gas production, ME, SCFA, and GY(24). We observed that 5% safflower grain in ruminants' diets did not negatively affect the in vitro cumulative gas production up to 96 h, T-DMD, true organic matter digestion (T-OMD), ME, net energy lactation (NEL), GY(24), PF24, and MCP values and SCFA compositions; but 10% and 20% levels negatively affected the in vitro gas production, ME, NEL, and SCFA values (p<0.05).The use of up to 20% hay and straw had no negative effect on the parameters (p>0.05). Using safflower grain, hay and straw in horse and ruminants' diets did not affect the in vitro methane production (p>0.05). Consequently, using up to 5% safflower grain, and 20% hay and straw has the potential as a feed source in the diets of horses and ruminants.