商業函件分兩部份，第一部份是 1930年至1969年間與聯益行業務相關的合約文件，包括各類保險單、商業登記證、代理許可證、還貨款協議、借據等。第二部份是商務信件，包括104 張戰時各地報道藥業生意情況的短箋、電報、通告和一本掛號郵件收據簿等。信件中除少量政府公函外，大部份是寫給幾位聯益行管理級人員的私人或商務信件，涵蓋1904年至1970年，共超過800張，按年份保存在檔案中。

This series is arranged into two subseries. Subseries (a) consists of contractual papers and agreements pertaining to the business activities of Luen Yick Hong such as insurance documents, business registration certificate, agent permit, payment for goods agreement, money lending slip etc. between 1930 and 1969. Subseries (b) is a collection of business correspondence comprising letters including 104 short notes reporting on the herb business situation in wartime, telegrams and a registered mail receipt book. Apart from a few government letters, the letter bulk is made up of a large quantity of personal and business-related letters addressed to some of the managing staff of Luen Yick Hong totaling more than 800 sheets from 1904 up to 1970. They are arranged in chronological order.