Aim of review:Through this review of observational study designs, we aim to advocate the use of non-interventional studies for clinical researches in anesthesiology. Method: We discussed the statistical considerations in selecting study design and the analysis. The major consideration is to reduce the bias and improvement efficiency. Reduction of bias through design (e.g.: randomization, matching etc.) is more preferable. However, a more objective design such as the randomized clinical trial is often not feasible. In this case, observational study designs accompanied with more advanced and complete statistical analysis can reduce the bias and improve efficiency. The cross-sectional, case-control, and cohort study designs are discussed with the advantages and limitations. Recent findings: With the rapid development of clinical researches in anesthesiology in past 15 years, observational studies are still yet to be understood and utilized. Summary: Through this review, we expect to raise more attention in the use of observational studies in clinical researches in the area of anesthesiology.