Despite being a promising biomass source for gasification, the practical use of rice straw in Vietnam is hindered by its low gasification efficiency. This study introduces an innovative approach by integrating the production of syngas and CO2 adsorbent during the gasification process of rice straw, departing from the conventional focus solely on improving gasification efficiency. Results showed that the gasification of rice straw, conducted in the 20 kWe commercial gasification system (PP20 All Power Lab), attained a thermal conversion efficiency of 58.7%. Syngas produced exhibited consistent composition, with CO and H2 content ranging from 12.1% to 15%, CO ranging from 16.9% to 22.1%, and CH4 ranging from 1.9% to 3.9% throughout the operation, demonstrating relative stability. Notably, a considerable amount of residual char, accounting for 22.1 wt% of the initial feedstock, was generated. Characterized by notable traits such as high surface basicity, aromaticity, and a dense concentration of (ultra-)micropores, the residual char demonstrates suitability for applications in CO2 adsorption. In controlled laboratory conditions (25 °C, 1 atm, without heat-mass transfer limitations), the adsorption capacity reached 1.2 mmol g−1. Transitioning to more practical conditions (40 °C, 1 atm, within a 2-cm adsorbent bed subject to diffusion constraints), the CO2 adsorption capacity of the residual char ranged between 2% and 4.8% of the adsorbent's weight, while the CO2/N2 selectivity measured between 25.5 and 29.7. These findings underscore the significant potential of integrating syngas and CO2 adsorbent production through rice straw gasification, indicating a promising avenue for sustainable energy and carbon capture technologies.