For offshore structures, especially jacket supported structure such as fixed platform and offshore wind turbine, the underwater area provides an ideal site for corrosion formation and marine fouling. In this marine environment, the structures are exposed to particularly aggressive corrosion and colonized by marine organisms involving a diversity of species. In this paper, a number of cases are conducted where an existing fixed platform is subjected to uniform corrosion. Furthermore, the platform is also subjected to marine fouling. The platform is assessed to investigate the effects of corrosion and marine fouling on its structural strength by determining the Reserve Strength Ratio (RSR) value. It is found the platform is limited to at least 50 years of service life when subjected to average corrosion. However, the platform is no longer considered as safe after 37 years when subjected to severe corrosion. Moreover, there is an RSR loss of 38 when marine fouling is introduced at the first 5 years which is detrimental to the overall safety of the platform. On the other hand, there is minimum RSR loss of only 5 for most cases when marine fouling is introduced but still detrimental to the overall safety of the platform. The obtained outcomes were documented and will be useful information to conduct condition assessment (or structural health monitoring) of aged fixed jacket structures. © 2019 Latin American Journal of Solids and Structures. All rights reserved.