Geochemical and geotechnical studies of the in-situ weathering deposits along the basement complex of Ado-Ilawe Road, South-western, Nigeria have been studied with aim of determining the suitability of the deposits for civil engineering construction. Five samples were taken from road cut site, at different horizons/depths based on colour and grain size variation with the aid of digger, shovel and spade. Chemical and geotechnical analyses were carried on the samples. The chemical analysis was carried out on the samples to determine the mineral oxides present in the samples. The geotechnical involved grain size distribution test, Atterberg limits test, specific gravity, linear shrinkage test, firing test, bleaching test, compaction test, water absorption determination, and California Bearing Ratio test (unsoaked). All the analyses were conducted according to British Standard procedures. The results of the chemical analysis revealed the predominant of over other oxides. The contents range from 63.2 to 68.4 %, ranges from 9.41 % to 15.3 %, and ranges from 5.21 % to 8.72 %. The analysis revealed the clay minerals are illites, and/or montmorillonite/illite derived from an acidic parent rock. Mineralogical characteristics and chemical trends indicate the increase in degree of maturity with depth. The geotechnical analyses show that liquid limit ranges from 48.5 to 55.0 %, plastic limit is between 24.0 and 31.40 %, linear shrinkage ranges from 0.5 to 1.60, the specific gravity ranges from 2.20 to 2.44. The bleaching test produced no colour change. The samples exhibit moderate water absorption potential, while the values obtained for modulus of rupture, compressive strength, and CBR are below standard for road/building construction, rated as fair to poor foundation material using AASHTO and USCS standard. However, the material fall within specification of ONORM 2074 (1990) as seal/liners for landfill. It is presume that the soil might require some amount of stabilization to qualify it for foundation material for building, road construction, and other civil engineering structural works. Keywords: Geochemical, geotechnical, bleaching test, firing test, montmorillonite