Background: This study represents Carapace length-weight (CLW) and Carapace width-weight (CWW) relationships with relative condition factor (Kn) for two commercially important portunid crab species of genus Charybdis viz., Charybdis feriata (Linnaeus, 1758) and Charybdis hellerii (Milne-Edwards, 1867) collected from the Gulf of Mannar, Southeast coast of India. 
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Methods: A total of 876 specimens were collected and measured for a period of one year from July 2022 to June 2023. The two species&rsquo; CLWR and CWWR were determined using the least square linear regression equation W= aLb, where &ldquo;W&rdquo; is body weight in gm, &ldquo;L&rdquo; for carapace length/width in centimetres, &ldquo;a&rdquo;, the intercept and &ldquo;b&rdquo;, the slope of the regression curve. Regression analysis was used to determine the parameters &ldquo;a&rdquo; and &ldquo;b,&rdquo; as well as their statistical significance and 95% confidence limits by using MS Excel. 
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Result: The slope (b) for the CLWR and CWWR of the species C. feriata is 3.2196 and 3.1901 respectively and for the species C. hellerii, the same was found to be 2.3427 and 2.3720 respectively. The relationship of the studied two parameters namely CLW and CWW were found to be significant for both the selected species at 1% level (P&gt;0.01).&nbsp; The Relative Condition factor (Kn) for the species C. feriata was determined to be 0.64 and 0.51 for CLWR and CWWR respectively and for the species C. hellerii, the same was found to be 1.45 and 0.86 respectively. The importance of studying the relationship in Portunid crab species with regard to the parameters carapace length and carapace width and the relative condition factor studies in the studied crabs were discussed and suggestion were also given for the management and conservation of the resources and selected species of Gulf of Mannar. This study presents the first reference on CLWR and CWWR for these species from the Gulf of Mannar along the Southeast coast of India. 
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Carapace Length/Width-Weight Relationships and Relative Condition Factor of Two Commercially Important Charybdis Species of the Gulf of Mannar, Southeast Coast of India