Monica e a Sereia do Rio is a 1987 Brazilian animated film directed by Mauricio de Sousa and Walter Hugo Khouri. It is the fourth film based on the Monica and Friends comic book series, created by Mauricio de Sousa. The film consists of four stories and features the participation of singer Tetê Espíndola, who appears in live-action alongside the animated characters. The scenes were filmed at the Rio Quente lodge in Goiás. For this movie, Mauricio followed the structure of his first feature film, dividing it into separate stories. The final segment, "A Sereia do Rio", was inspired by an animated short from the early 1980s, originally intended for broadcast on TV Globo.

Monica e a Sereia do Rio was released in theaters on February 7, 1987, and was later re-released on VHS on at least two occasions. The film received mixed reviews from critics; while it was recommended for children, technical aspects, acting, and costumes were subject to criticism. It was screened at the Gramado Film Festival and the Brasília Festival of Brazilian Cinema. Additionally, its behind-the-scenes production was adapted into a comic strip for Monica magazine.