Introduction Gram staining was developed by Christian Gram in the 1800s, a Danish bacteriologist. (Smith and Hussey, 2005) This was the first and most commonly used differential staining technique in microbiology. Additionally, bacteria are transparent and cannot be seen under a microscope. For this reason, Gram stain is an important tool to distinguish two main types of bacteria, Gram-positive and Gram-negative. Gram staining differentiates between Gram positives and Gram negatives based on their cell wall structure. (Menard, et al., 20150) Most Gram-positive or Gram-negative bacteria, but there are a few Gram-variable bacteria and very small bacteria without a cell wall that does not have a Gram reaction. For the purposes of this laboratory, we focus on the two main types of bacteria Gram+ and Gram-. Bacteria are prokaryotes that have a cell wall; they are classified into bacillus (rod-shaped), Coccus (spherical) and Spirillum (spiral) (Menard, et al., 2015). Therefore, in this laboratory, we will examine whether after using Gram staining techniques, Gram-positive bacteria turned purple and Gram-negative bacteria turned pink, showing the difference between the characteristics of each bacteria. Then, by observing the morphological characteristics of the bacteria, under a bright field microscope, Citrobacter freundii a Gram-positive bacteria and Staphylococcus aureus a Gram-negative bacteria. We also learned what can go wrong when using Gram stain and produce errors in testing. Therefore, we witness the different results that occur when too much bleach is added or when the glass slide is improperly heat set. Learning Gram stain techniques helped us understand how bacteria can be identified for proper treatment and for future studies on bacteria.