This study was aimed to improve team effectivity by giving assertive communication training to the commercial division. The type of study was action research. The samples were obtained using a purposive sampling technique due to specific criteria given for sampling. The sample size in this study was 9 commercial division employees. Team effectivity was measured using the questionnaire, interviews, and observation. The tool used to collect data was team effectivity questionnaire of “Five dysfunctions of a team” from Lencioni (2002) which comprised of 38 items consisted of five characteristics, i.e. trust, conflict, commitment, accountability, and result, with validity and reliability value of α 0.894, which means that all items were reliable in predicting criteria. The data analysis technique used to determine training needs was the Microsoft Excel program adjusted to calculation from Lencioni. The results showed that trust and accountability aspects were in the medium category, whereas conflict, commitment, and result aspects were in the high category. These results indicated that trust and accountability should be developed through assertive communication training. This study is expected to be a consideration for further studies.