This study was aimed to determine the effects of different additives and lignin peroxidase (LiP) enzyme on the in vitro gas production and methane production of some straws. The study involved 8 groups for each forage, 3 different straws (wheat straw, soybean straw, sorghum straw), which comprise of 2 different LiP enzyme treatments (Available –Not Available) and 4 different treatment groups (control, 4% urea, 10% molasses and 14% urea+molasses (4% urea, 10% molasses). Hohenheim gas test was used in in vitro gas production measurements while infrared methane analyzer was used to determine methane production. The experiments were conducted as per the randomized factorial design in randomized complete blocks. In terms of crude protein content, the highest CP was obtained from the urea+molasses treatment for wheat, sorghum and soybean straws, while control groups were found to have the lowest CP content. The lowest NDF, ADF and lignin contents were found in sorghum straws (P<0.001). The highest gas production value was obtained from sorghum straws for 24-hours incubation process (P<0.001). Treatments did not cause any effects on 24-hours gas production for straws without enzyme addition (P>0.05). LiP enzyme was found to increase in vitro gas production and methane production for all straws and treatments (P<0.001). As a result, sorghum straws were proven to offer a higher feed value and additional in vivo and in vitro studies are required with the aim of determining the possibilities of using LiP enzyme in forages.