This invention relates to a process for co-producing methanol and ammonia, wherein a syngas mixture consisting essentially of carbon monoxide (CO), carbon dioxide (CO2) and hydrogen (H2) is first partially reacted in a methanol once-through reactor, unreacted syngas is divided into a first and a second stream, the first stream is purified and fed to an ammonia synthesis section, and the second stream is fed to a methanol synthesis and purification section. With this process it is possible to produce methanol and ammonia at very high capacities in an integrated single process, applying unit operations not exceeding current practical capacity limitations. For example, the process allows production of 8000 mtpd of methanol and 2000 mtpd of ammonia starting from natural gas and air. The process further shows a balanced production of ammonia and carbon dioxide, thus allowing co-production of urea also to be integrated.