The purpose of this study is to investigate Indigenous pupils' achievement in Mathematics with Bilingual (Bahasa Melayu and Temiar) versions of mathematics tests. Both tests were based on Mathematics computation and word problem items. This study involved eight Orang Asli (Indigenous) primary students from eight schools in the district of Sungai Siput, Perak. A total number of 230 Grade 5 (11 years old) pupils participated in the study. Difficulty index was used to measure pupils' achievement in mathematics computation and word problem items involving Bahasa Melayu and Temiar (the Orang Asli native language). 50 Multiple Choice Items (MCI) were administered in two languages which were the Malay language and Bilingual (Malay and Temiar) languages, where the Temiar language is the Orang Asli's language in the oral form. The oral form of the Temiar language was translated from the Malay language by Temiar native language experts, which were then audio recorded by the researchers. The study provide evidence that the Bilingual test version that used Temiar language is easier for the pupils and this version had also improved Grade 5 pupil's achievement in mathematics word problems items in. It is conjectured that the Orang Asli pupils' performance in the computation test is better than the word problem items in Mathematics.