| Sugar Is Not Sweet | |
| Director: | Rattana Pestonji |
| Producer: | Rattana Pestonji |
| Starring: | Sombat Metanee Metta Rungrattana Saneh Komarachun Preeya Rungreuang Sompong Pongmit Sarinthip Siriwan Ruj Ronnapop |
| Music: | Preecha Mettrai |
| Cinematography: | Sunt Pestonji |
| Editing: | Rattana Pestonji |
| Released: |  1965 |
| Runtime: | 138 minutes |
| Country: | Thailand |
| Language: | Thai |
Sugar Is Not Sweet (Thai: น้ำตาลไม่หวาน or Namtarn mai warn) is a 1965 Thai romantic comedy film written and directed by Rattana Pestonji. It was the director's final feature film. The film was featured in a retrospective program to the director at the 2005 Pusan International Film Festival.
Chaokun Charoenkesa, the owner of a shop that sells hair-loss treatments, wants to pay back his debt of kindness to a friend, whose formula is responsible for the Chaokun's prosperity. So he arranges for his good-for-nothing son, Manas, to marry Sugar, the daughter of his dear friend.
Rattana Pestonji has a cameo appearance in this film as the doctor who treats Chaokun in his moment of death.