The proteome is an abundant source of potential therapeutic targets, and a comprehensive evaluation of proteins as therapeutic targets for a wide range of diseases is required. By screening 4,907 plasma proteins, we conducted a systematically two-sample proteome-wide Mendelian randomisation (MR) study to uncover potential therapeutic targets for 16 clinical diseases. Following MR analysis and stringent process filtering, a total of 79 causative plasma proteins (false discovery rate<0.05) were discovered. Colocalization analysis (Posterior Probability H4>0.8) further supported the causality of three proteins (MAP2K1, GFRA1, and THBS3) in gastroesophageal reflux disease; LYPLAL1 in keratoconus; three proteins (PCSK9, ANGPTL4, and GCKR) in familial hyperlipidemia; CRAT in atopic eczema; three proteins (IRF3, CA12, and TNFRSF1B) in hypothyroidism; AIF1 in age-related hearing impairment; and SCARF2 in alopecia. Interestingly, having a genetically higher circulating CA12 level is associated with a lower risk of hypothyroidism (OR=0.47, p-value=1.68e-05, Posterior Probability=0.82). Single-cell RNA sequencing analysis showed that CA12 was mainly expressed in fibroblasts and epithelial cells in patient thyroid tissue and that its expression increased in older adults. Furthermore, with a proportion of 3.8%, hypothyroidism appears to mediate the effect of IRF3 on idiopathic pulmonary fibrosis, according to mediation analysis. Overall, our research could provide new insights into the etiology of clinical diseases as well as intriguing targets for the development of screening biomarkers and therapeutic treatments.