Blood levels of progesterone (P₄), estradiol-17β (E₂), calcium (Ca), triglyceride (TG), and total protein (TP) were monitored in a captive female loggerhead turtle throughout a nesting season that included three 13- or 14-d internesting intervals. We observed the turtle's ovaries to monitor the appearance of shelled eggs, using ultrasonography, and compared the results of blood analyses and ovary observations. The blood P₄ level remained low (<0.2 ng/mL), with the exception of three sharp peaks (1.7, 2.2, and 4.2 ng/ mL) immediately after the initial three nestings. Eggshell formation occurred immediately after the P₄ peaks. The blood Ca level gradually dropped to approximately 3.0 µmol/mL during each eggshell formation period but then recovered to approximately 3.7 µmol/mL prior to the next eggshell formation. The blood E₂ level fluctuated between 44 and 299 pg/mL, but with two higher peaks (734 and 419 pg/mL) after eggshell formation in the first and second internesting intervals, respectively. During the nesting season, the blood TG level (initially 20 µmol/mL) showed a stepwise drop to 7.6 µmol/mL, while the blood TP level fluctuated between 57 and 69 mg/mL with no distinct peaks. The periodic cycle of P₄ and Ca changes aligned with albumen layer secretion around ovulated follicles immediately after nesting, followed by eggshell calcification in the clutch. The relatively small fluctuations in E₂, TG, and TP during the nesting season suggested that lipid deposition and preovulatory follicular development were completed prior to the start of nesting.