Bacterial endophytes play a vital role in the growth and fitness of host plants from infection by phytopathogens. To our knowledge, however, little information is available on the endophytic bacterial composition in healthy and diseased Kappahycus alvarezii, one of the most important major sources of carrageenan industries, especially in Sabah. The main idea was to analyze and compare the composition of endophytic bacterial communities in healthy and diseased K. alvarezii isolated from Sabah, Malaysia. The data reveals the composition of endophytic bacterial microbiomes in healthy and diseased K. alvarezii isolated from Sabah. The isolated endophytes were identified using 16S rDNA sequencing. Taxonomic identification and phylogenetic tree analysis were done using the online BLAST (blastn) and MEGA11 software, respectively. The data presents the diversity of bacterial endosphere microbiomes found in healthy K. alvarezii which are composed of Bacillus, Cytobacillus and Priestia whereas Vibrio and Micrococcus occurred exclusively in the diseased K. alvarezii. Microbial comparative analysis between the healthy and diseased seaweed points to the potential of several Bacillus strains that may have biocontrol potential against Vibrio infection in seaweed such as the ice-ice disease. Raw data files are available at the GenBank, NCBI database under the accession number MZ570560 to MZ570580.