Provided are a rubber composition in which microfibrillated plant fibers are sufficiently uniformly dispersed to improve tire performance requirements in a balanced manner, and a pneumatic tire formed from the rubber composition. The present invention relates to a rubber composition formed from a masterbatch containing a rubber latex and microfibrillated plant fibers, the masterbatch being obtained by stirring the microfibrillated plant fibers in a solvent with a circulation type or continuous homogenizer and mixing the resulting microfibrillated plant fiber solution with the rubber latex and a cationic polymer, the microfibrillated plant fibers having a mean fiber length of 10 to 150 μm, the microfibrillated plant fiber solution containing 0.1 to 2.0% by mass of the microfibrillated plant fibers, and the amount of the cationic polymer being 0.01 to 5 parts by mass per 100 parts by mass of the rubber component of the rubber latex.