There is a diversified microbial ecosystem in the rumen for efficient utilization of diet by providing essential nutrient to their host. But there are different factors affecting rumen microbial protein synthesis which are physical factors, chemical factors, dietary factors, biological factors and endogenous factors. Among the details of factors, dietary factors and ruminal pH are the dominant factors influencing rumen microbial protein production. The effects of some dietary factors, on the amount and efficiency of microbial protein synthesis, are discussed in this review. Specifically, these factors include forage quality diets, level of feed and types of feed. It seemed that diets containing a mixture of forages and concentrates increase the efficiency of microbial protein synthesis because of an improved rumen environment for the growth of more diverse bacterial species. This review describes physical and chemical factors which include: pH and buffer system, oxygen concentration, rumen outflow rate and synchronized release of nitrogen and energy from the diet, a nitrogen compound, energy spilling, vitamins and minerals and antimicrobials chemicals, respectively. Age, species, physiological status, sex, and stress are among endogenous factors that mostly affect microbial protein synthesis of a ruminant. Bacteriophages, protozoa predation and bacterial lysis are biological factors affecting the efficiency of microbial protein synthesis. All these factors have a direct effect on the synthesis of microbial protein in the rumen. Therefore, the cumulative effects of the above factors are resulted in the depopulation of rumen microflora and finally reduction of animal product. So, improvement in quantitative aspect of microbial protein synthesis solves many problems from simple to complex so that, the quantitative aspect of rumen microbial biomass are invaluable for health and productivity of ruminants than qualitative aspect hence, maintain health rumen ecosystem means having healthy ruminant.