The major purpose of this paper was to identify the word formation problems in the written English of Senior Secondary Schools 111 (SSS3) students. The main grammatical description used as a basis for this investigation is drawn from Ouirk et al (1972). The data for the paper were drawn from the essays written by 300 SSS3 students in six selected secondary schools from Ilesa West Local Government, Ilesa East Local Government and Atakumosa West Local Government Areas in Osun State. The essays were then analyzed for evidence of word formation Problems in their written English. This study found out that the pupils had problems with the different morphological processes in English. There was however variation in the level of use and the problem that arose with each of the morphological processes highlighted. In conclusion, on the basis of the findings of this study, suggestions that can lead to improvement in the teaching of word formation processes in English to Nigerian Secondary School pupils have been provided.