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This study aims to develop and produce scientific communication skills assessment instruments in valid X class high school physics learning. This research is a development research using 4D model. This research is done through 4 stages, which are (1) analysis phase, (2) planning stage, (3) development stage, and (4) distribution stage. Assessment instrument contains a description of the theory, the definition of the concept of operational definition, grating instrument skills assessment scientific communication, assessment sheets skill scientific communication, assessment rubrics, guidelines for scoring, and the recapitulation of the value of communication skills scientifically validated by experts and tested. From the results of validation experts obtained average percentage of 75,55% which indicates the criteria of scientific communication skills assessment instrument is very valid. This instrument was tested on 32 students of class X MIA 1 in SMA N 3 Demak and conducted by 1 physics teacher. The results of the test show that the percentage of products developed based on response or responses obtained average percentage of 88,83% with very valid criteria. Meanwhile, the validity of the analysis results showed that there were 4 (9,3%) item statement is not valid because r_xy <0,35, whereas 39 (90,7%) Other statement items are valid with r_xy> 0,35. Invalid statements include item number 24, 29, 36, and 43. On reliability analysis showed the value of r_count = 0,84432, while r_table = 0,35. From the analysis of the reliability values obtained r_count > r_table it can be concluded that the assessment instruments already reliable scientific communication skills.