This study aims to investigate the effects of warm up tasks as classroom activities on foreign language written production. For showing these effects, sixty out of one hundred forty Iranian sophomore EFL students from the Islamic Azad University of Lahijan branch, Iran were selected after following the Oxford Placement Test (OPT). Then, they were randomly divided into two groups; the experimental group who received the treatments on warm up tasks, and the control group who received a placebo. Both groups had to write two paragraphs of about 150 words that were considered as their pretests and posttests. The paragraphs were corrected by three experienced raters. Their scores analyzed through SPSS by applying Independent t-test, and Paired sample t-test. The findings revealed that participants in the experimental group, who had received the treatments on warm up tasks, significantly enhanced better performance in a writing test.