The effects of important practical parameters, specifically feedstock heterogeneity and heat-mass transfer on steam gasification of rice husk were investigated and quantified. Through proximate and ultimate analysis of ten rice husk types, the heterogeneity was expressed not only between different types but also within the same rice husk type. TGA-DTG curves showed notable differences in the thermal behaviors of rice husk during pyrolysis. The time required to gasify the same quantity of rice husk can vary in a ratio of 1–1.5 depending on the type. The Si content in rice husk showed an inhibitory effect to the char reactivity during steam gasification. An empirical factor of 1.3 could be applied to the conversion rate of rice husk for every 1-cm increase in the bed thickness. Results of this study could contribute to the improvement of existing systems or the design of new efficient rice husk gasifiers.