Sidney Lau romanisation is a system of romanisation for Cantonese that was developed in the 1970s by Sidney Lau for Cantonese textbooks, glossaries, and dictionary.

Lau's romanisation indicates tonality with superscript numbers, so no diacritics are required.^[1] He uses an English style of writing the vowels, as had some romanizations before him.^[2] His system was a plain attempt at simplification^{[citation needed]} which proved popular with western learners of Cantonese as a second language^{[citation needed]} and was initially the system of romanisation adopted by the University of Hong Kong.^[2] However, the university now employs the Jyutping system for its Cantonese courses.^[3]

In his system, Lau treats /ɵ/ and /o/ as allophones of one phoneme represented with "u", while they are often respectively regarded as allophones of /œ:/ and /u:/ in other systems.^[4]

1° indicates the high flat tone. If ° appears after any other tones, it signifies a changed tone and that the word is to be pronounced as 1°, but 1° is not the original/normal tone of the word. Similar to °, if * appears after any tones apart from tone 2, it indicates that the word is to be pronounced as tone 2, but tone 2 is not the original/normal tone of the word.^[5] When the asterisk and small circle are applied to a superscript number, they are not superscripted further.^[6]

• Comparison of Cantonese transcription systems

• Explanation of Sidney Lau's Cantonese Romanization System
• Cantonese writing, with information on Sidney Lau romanisation