The aim of this work was to identify main plant growth regulators (PGRs), such as, indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellic acid (GA), zeatin, kinetin and 6-benzyl amino purine (BAP) and to determine corresponding quantity in nine seaweed varieties. The samples were extracted by methanol-water (75%) solvent from lyophilized seaweeds for 16 h at -20 degrees C. A rapid and sensitive UPLC-MS/MS method was developed and validated. Both individual and mixed standards were used to study the peak separation and identification of hormones. The precision of the method was tested with good RSD values of 0.67-2.01 for intra-day and 1.21-3.50 for inter-day in six and four replicates, respectively. Accuracy was in the range of 82.75-98.94% by spiking phytohormone standards to eliminate plant matrix. Excellent linearities were found within the ranges of 0.5-50 ng mL(-1) for zeatin and 0.5-10 ng mL(-1) for BAP, 5-500 ng mL(-1) for GA and kinetin, and 2.5-500 ng mL(-1) for IAA and ABA. The results showed that the applied SPE-UPLC-MS/MS method was very sensitive and can be used extensively for the routine analysis of trace amounts of multi-class phytohormones in seaweeds. The method developed greatly reduced both sample preparation and total analysis time.