The present paper deals with the preparation of 2-hydroxymethyl-cis-cyclohexylidene acetic acid (Ⅲ) and its lactone (Ⅱ) and also with the conformation of the modified structural formula Vc for the Mannich-Braun compound^[3]. The mechanism of the formation of (Vc) has been briefly discussed. 2-Hydroxymethyl cyclohexylidene acetic acid lactone[Ⅱ, m.p. 62-62.5°, λ_max^EtOH 222 mμ (ε 13,100)] was obtained together with the Mannich-Braun comppund (m.p. 150.5-151.0°) from 2-acetoxymethyl cyclohexanone (Ⅳ) by the Reformatsky reaction. Based upon new evidences from the UV- and IR-absorption spectra and from the results of periodic acid oxidation, the modified structure of the Mannich-Braun compound (Vc) has been confirmed. On saponification with diluted alkali followed by acidification, (Ⅱ) was converted into the 2-hydroxymethyl-cis-cyclohexylidene acetic acid[(Ⅲ), m.p. 109一110°, λ_max^EtOH 220 mμ (ε 11,100), of which the structure is supported by the results from investigations on the UV- and IR-absorption spectra and on the cyclization by means of heat or acid. With diazomethane, (Ⅲ) gives methyl 2-hydroxymethyl-cis-cyclohexylidene acetate (ⅩⅠ). Acetylation of ⅩⅠ produces methyl 2-acetoxymethyl-cis-cyclohexylidene acetate[(ⅩⅡ), b. p. 106-108°/0.2 mm; n_D¹⁶ 1.4887,λ_max^EtOH 221 mμ (ε 12,800)], which yields Ⅱ again on treatment with concentrated hydrochloric acid. With 3,5-dinitrobenzoyl chloride, (ⅩⅠ) forms methyl 2-(3',5'-dinitrobenzoxymethyl)-cis-cyclohexylidene acetate [(ⅩⅢ), m.p. 100.5-101°]. Partial hydrolysis of (ⅩⅢ) with concentrated sulphuric acid gives 2-(3',5'-dinitrobenzoxymethyl)-cis-cyclohexylidene acetic acid [(ⅩⅣ), m.p. 188-189°], which has been reconverted into (ⅩⅢ) by esterification with diazomethane.