Whole rock carbonates samples from the Aptian to Middle Albian deposits of the Pădurea Craiului Mountains were analysed for carbon and oxygen isotopes. The data defines the first continuous stable isotope baseline trends of the Early Cretaceous in the Western Romanian Carpathians (Apuseni Mountains). During the Late Jurassic to the Late Cretaceous Pădurea Craiului was part of a larger carbonate-platform belt which developed in the Thetyan region. The isotope data provides opportunities to recognize the presence of two major δ¹³C positive excursions that have been attributed to the OAE1a (upper part of Ecleja Formation and Valea Măgurii Formation) and 1b (Vârciorog Formation – Subpiatră Member). From a background of 2 – 3‰, a significant δ¹³C negative excursion to values as low as 0.46‰ has been recorded in the early Aptian preceding the OAE1a. A second major δ¹³C negative (0.74 ‰) excursion was found in the shale deposits of the basal part of the Vârciorog Formation (Late Aptian) and has been assigned to the Fallot major δ¹³C perturbation. The lower part of the Subpiatră limestones (Late Aptian – Albian) are characterized by lower δ¹³C values (from 2.95 to 2.97‰) as compared with the values recorded in their upper part (from 3.75 to 4.70‰). Such a considerable increase of the δ¹³C values from 2.95‰ to 4.70‰, followed by a small drop down to 3.75‰, and then another increase up to 4.23‰ is characteristic to the OAE1b. Large fluctuations of δ¹⁸O values between -2.37 and -9.58 ‰ suggest a warming episode during Early Aptian followed by a cooling trend in the latest Aptian-Early Albian.