The purpose of this study was to explore the comparative effects of playing field size on accurate decision making skills of football performance at Bahir Dar city Ethiopia. The total subject for the study were fifty two (n =52) male football trainees of two Bahir Dar city u-17 male football project players in Ethiopia 2014 E.C. all players are taken as a sample by using comprehensive sampling technique. Experimental research design and quantitative research approach were employed. Before the intervention both comparative groups compute a match out of their training field site at Bahir Dar university sport academy stadium as a base line purpose only. Both the comparative experimental groups performed ten week 40 minute duration training game 2 days per week. After the intervention post match competition was computed out of their training site at Bahir Dar university sport academy stadium again. The data was collected by using a CANON 5D Mark iv camera during a match and decision making skills of selected skills ( i.e. passing decision, receiving decision, dribbling decision and shooting decision) were counted and tallied by three experienced football experts. The data was analyzed by paired sample t-test and independent sample t-test with SPSS version 26 at significance level of 0.05. Based on the analyzed data, small field size training group during post match, decision making skill of shooting showed significant deference than large field size training group (p<0.05). On the other side, both comparative group shows no statistical difference in the other three decision making skills (i.e. passing decision, receiving decision, and dribbling decision p>0.05. In conclusion, training in different filed size have no significance difference in decision making skills of passing, receiving, and dribbling during 90-minute match of u-17 male football project players. However, training in small field size improves decision making skill of shooting than playing in a large field size during 90-minute match. Therefore the study recommends that coaches should give emphasis to small sided games as a training to improve trainees’ decision making skill in a game.