Influence of sample sizes on analyzing community parameters of periphytic diatoms was studied in coastai waters of the Yellow Sea from May 2010 to June 2010. Sampies were coiiected from two depths of 1 m and 3 m using an artificial substrate. Based on a 95% probability, 15, 8, and 5 replicate slides (~260, 140, and ~90 cm^) were sufficient for recovering the diatom communities with specified cumulative contributions of 99%, 95%, and 90% at two depths, respectively. To achieve less than 10% standard errors (coefficients of variation), six (105 cm^) replicate slides were required for biodiversity analysis of the microperiphyton communities with various colonization times at two depths. More replicate sides were required for the young diatom communities (less than 14 days) than the mature samples (greater than 14 days). These results suggest that six replicate slides at two depths may be sufficient to analyze community parameters of periphytic diatoms in costal waters. Water Environ. Res., 85, 2228Res., 85, (2013.