The lignocellulosic biomass found in rice straw (Rs) is considered the most effective for anaerobic digestion. Biotransformation of Rs is slowed down by the resistant lignocellulosic fraction, which also acts as a rate-limiting step in the process. However, this study investigated the influence of pretreated Rs (1% NaOH, w/v) with food waste (Fw) in eight different compositions which are as follows: case-a (control); case-b: 2% treated rice straw (trs), case-c: 3% trs, case-d: 4% trs, case-e: 5% trs, case-f: 6% trs, case-g: 7% trs, and case-h: 4% untreated rice straw (utrs) for enhanced biogas production at mesophilic temperature (35 ± 2 °C). A mixture with 4% w/v (Rs: Fw) significant (P < 0.05) biogas production as compared to other digested groups. After 28 days, maximum biogas production was still found in case-d (11,409 ± 188 ml) as compared to case-a (control, 7185 ± 141 ml), other alkali treated (case-b to case-g, 11,094 ± 17 ml to 6750 ± 295 ml), and case-h (10,480 ± 120 ml) mixed feedstock groups. Pretreatment with alkali seems to affect the Rs more with a significant decrease lignin and increase in cellulose content. A higher VS/TS ratio signifies a greater organic content, which is desirable for the production of biogas and methane. However, the synergistic effect of Rs and Fw emphasizes the need for correct proportion in increasing biogas yields. These results provide valuable insights into optimizing biogas production through the effective utilization of alkali-treated Rs.