The objectives of this research are to find out whether (1) Video is more effective than picture slide in teaching writing to the eighth grade students of SMP Negeri 4 Karanganyar; (2) students who have high interest have better writing skill than those who have low interest; and (3) there is an interaction effect in teaching writing between teaching media and students‘ interest on the students‘ writing skill. The research method used in this research was an experimental research. The independent variables of this research are Video and Picture Slide and the dependent variable is writing skill. In addition, Interest as the attributive variable is divided into two levels namely high and low interet. The population of the research was the eighth grade students of SMP Negeri 4 Karanganyar in the Academic Year of 2012/2013 which consisted of eight classes. There were 32 students for each class. The samples were two classes taken by using cluster random sampling. The experimental class was taught using Video and the control class was taught using Picture Slide. The data were obtained from interest questionnaire and writing test. The scoring data from writing test were collected after the students of both samples got eight times of treatments. The researcher analyzed the data using ANOVA (Analysis of Variance) and Tukey test. The results of the research are: (1) Video is more effective than Picture Slide to teach writing to the eighth grade students of SMP Negeri 4 Karanganyar; (2) students with high interest have better writing skill than those with low interest; and (3) there is an interaction effect in teaching writing between teaching media and students‘ interest on the students‘ writing skill. Based on the research findings, it can be summarized that Video is an effective media to teach writing and the effectiveness of this media is affected by the level of interest. For the students having high interest, Video is more effective than Picture Slide. For the students having low interest, Picture Slide gives a better effect on the students‘ writing skill. Thus, the usage of Video in teaching writing is effective to establish the students‘ writing skill. Keywords: Video, picture slide, writing skill, interest, experimental study.