<p>This article presents an improved bias current cancellation circuit (IBCCC) used for high precision amplifier that is featured by low input bias current and low offset voltage. This type of operational amplifier is mainly used in high precision instruments. IBCCC is added a CE voltage clamping structure which greatly reduce input bias current, compared to traditional one. Besides, this circuit uses trimming resistor to suppress offset voltage and drift. The amplifier consists of four modules: biasing, input amplifier, bias current cancellation circuit and output stage. Biasing network adopts cross-coupled structure to improve the precision of mirror current. This device is fabricated using the standard bipolar IC process. Measurement results show that the input bias current is less than 1.0nA, the typical values of offset voltage and drift are 3.4<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\upmu \)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">μ</mi> </math></EquationSource> </InlineEquation>V and 0.027<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\upmu \)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">μ</mi> </math></EquationSource> </InlineEquation>V<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(/^\mathrm{{ \circ }}\mathrm{{C}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mo stretchy="false">/</mo> <mo>∘</mo> </msup> <mi mathvariant="normal">C</mi> </mrow> </math></EquationSource> </InlineEquation> respectively. Compared to the amplifier with bias current cancellation structure similarly proposed by Kim, Hyungseup et.al., the input bias current of this paper is decreased by more than 95%, therefore the improved structure in this paper has obvious advantages.</p>