Background: Malaria is the major public health problem in Ethiopia. Rain fall amount and distribution have impact for malaria transmission. Objective: To assess the relationship between positive malaria cases and Rainfall within ten year’s periodic trends of malaria transmission. Method: Retrospective study design was conducted by using ten years monthly rainfall and positive malaria cases. Simple linear regression, correlation were applied to analyze association. SPSS version 16.0 was used for analysis. Result: A slight variation of malaria transmission was observed in the last ten years and the transmission was non periodic. Among Plasmodium species, P. falciparum was highly prevalent. From spearman correlation analysis monthly minimum rainfall (p=0.022) at one month lag was significantly correlated with total positive malaria cases. Simple linear regression analysis suggested that monthly rainfall (p=0.001) at one month lag was significant meteorological factor. Multiple linear regressions analysis also showed that, rainfall had significantly (p<0.001) correlated at the same time with positive malaria cases by stepwise regression. Conclusion: From this finding, malaria transmission was not seasonal. Rainfall has association with malaria cases and may effect on the same or next month malaria cases occurrence. Rainfall seems best malaria predictor, since strongly correlated with malaria cases.