This study aimed at identifying the effect information system efficiency on effectiveness of decision making in Algerian banks. And to achieve the study objectives, A questionnaire was developed and distributed, which consist of (50) subjects, (45) questionnaire of which were returned and analyzed. Validity and reliability of questionnaires were computed. The results of the study refer to significant statistical effect of information system competency on effectiveness of decision making in banks sample study. The study attains the following results: Relational Relations between Variables:  There is significant positive correlation between the efficiency of information systems and the effectiveness of decision-making at the level of significance (0, 01). There is significant positive correlation between the dimensions of the information systems efficiency (quality of the hardware used, suitable information, the efficiency of workers), and the dimensions of the effectiveness of the decision-making (quality of decision, the time of decision-making, ease of decision-making, taking into account the acceptance of the resolution by the staff) at the level of significance (0, 01). Effect Relationships between Variables: The quality of the hardware used in the information system affect positively and significantly on the effectiveness of the decision-making. There is positively and significantly affect of the suitability of the information on the effectiveness of the decision-making. The efficiency of workers in the information system affect positively and significantly on the effectiveness of the decision-making.  In the light of the findings; some recommendations are given.