In this series, we investigate quantum ergodicity at small scales for linear hyperbolic maps of the torus ("cat maps"). In Part I of the series, we prove quantum ergodicity at various scales. Let N = 1/h, in which h is the Planck constant. First, for all integers N ∈ N, we show quantum ergodicity at logarithmical scales | log h| −α for some α > 0. Second, we show quantum ergodicity at polynomial scales h α for some α > 0, in two special cases: N ∈ S(N) of a full density subset S(N) of integers and Hecke eigenbasis for all integers.2010 Mathematics Subject Classification. 35P20, 58G25, 81Q50, 37D20, 11F25. Key words and phrases. Hyperbolic linear maps of the torus, quantum ergodicity, small scale.