This study analyzed the code alternation and multimodality in FB interaction among high school students for the School Year 2019-2020. It analyzed the code alternation and multimodality in FB interaction among high school students for the School Year 2019-2020. It utilized a descriptive research design using qualitative and quantitative methods of research. There were 65 excerpts of Facebook interactions utilized as the main data of this present research. Conventional content analysis was used to gain qualitative data while frequency count and percentage were used to obtain quantitative data. Grade 10 students used multilingual posts using English-Filipino, Bicol Sorsoganon – English, Bicol Sorsoganon-English-Filipino and Bicol Sorsoganon – Filipino. Students used unconventional linguistic features in their writing system in the Facebook interaction, namely: non-standard orthography (spelling, capitalization and punctuation); letter-number homophone; and acronym, shortening and cyberslang. Likewise, the use of multimodal in the Facebook interaction was also noted such as emojis and reactions available to chats and Facebook, and pictures and memes to support ideas or content. Grade 10 students may be provided with varied purposeful activities in and out of the classroom to become an avenue to enhance their language proficiency and be creative in their language when using Facebook in their interaction. The language proficiency of the Grade 10 students may be enhanced to give them other strategies that they can use to be creative and efficient in communicating their ideas and contents in the Facebook interaction. The proposed output may be utilized to enhance the level of language proficiency of the students with the aid of social media such as FB as a learning avenue among high school students. Future research may be conducted to further investigate the occurrence of language use, code alternation and multimodality in the FB interactions or other social media used for their academics or teaching and learning interaction.