Little research has been conducted in the field of alternative assessment including portfolio and peer assessment in Iran. Moreover, In spite of the assumed advantages of portfolio and peer assessment, the practicality of these techniques needs to be investigated. To this aim, a total of 207 writing papers from 69 participants were collected to investigate the effects of peer and portfolio assessment on the writing components in two experimental groups. The data were collected from students of a general English semester course held at Sharif University of Technology. There were two experimental groups of 37 and 32 students experiencing portfolio and peer assessment respectively. As the treatment, students were supposed to write compositions, and for each composition, they were supposed to invest at least twenty minutes on a topic of interest e.g. sport, science, social issues, etc. And they were then rated by their teacher in group A and their peers in group B based on ten pre-established assessment criteria in each session during the term. After administering the writing post-test, independent t-tests were run to find the differences between the two groups. As the result, it was indicated that portfolio and peer assessment had the same effect on four of the five components of writing namely as content, organization, language use and vocabulary. But only there was a significant difference between portfolio and peer assessment groups on the last component of the study: mechanics in writing. The findings of this study have implications for language teachers, material designers, and educational policy makers.